Gas washout vent for patient interface

ABSTRACT

A gas-washout vent includes a housing with a first wall with one or more passages through the wall configured to provide fluid communication with a portion of the patient interface system exposed to a therapy pressure. The passages include respective first openings on a first surface of the first wall. The housing at least partially defines a second opening in communication with ambient atmosphere. A diffusing material is located at least partially within the housing to be adjacent the first surface. A surface of the diffusing material facing the first surface is spaced away from the first surface by a gap that extends to provide a fluid communication between all of the first openings and between all of the first openings and the second opening. The housing is configured so that air is prevented from flowing out of the housing at all areas directly opposite each of the first openings.

This application is the U.S. national phase of International ApplicationNo. PCT/AU2017/051231 filed Nov. 9, 2017, which designated the U.S. andclaims the benefit of U.S. Provisional Application No. 62/420,678, filedNov. 11, 2016, the entire contents of each of which are herebyincorporated by reference.

1 BACKGROUND OF THE TECHNOLOGY 1.1 Field of the Technology

The present technology relates to one or more of the detection,diagnosis, treatment, prevention and amelioration of respiratory-relateddisorders. The present technology also relates to medical devices orapparatus, and their use.

1.2 Description of the Related Art

1.2.1 Human Respiratory System and its Disorders

The respiratory system of the body facilitates gas exchange. The noseand mouth form the entrance to the airways of a patient.

The airways include a series of branching tubes, which become narrower,shorter and more numerous as they penetrate deeper into the lung. Theprime function of the lung is gas exchange, allowing oxygen to move fromthe inhaled air into the venous blood and carbon dioxide to move in theopposite direction. The trachea divides into right and left mainbronchi, which further divide eventually into terminal bronchioles. Thebronchi make up the conducting airways, and do not take part in gasexchange. Further divisions of the airways lead to the respiratorybronchioles, and eventually to the alveoli. The alveolated region of thelung is where the gas exchange takes place, and is referred to as therespiratory zone. See “Respiratory Physiology”, by John B. West,Lippincott Williams & Wilkins, 9th edition published 2012.

A range of respiratory disorders exist. Certain disorders may becharacterised by particular events, e.g. apneas, hypopneas, andhyperpneas.

Examples of respiratory disorders include Obstructive Sleep Apnea (OSA),Cheyne-Stokes Respiration (CSR), respiratory insufficiency, ObesityHyperventilation Syndrome (OHS), Chronic Obstructive Pulmonary Disease(COPD), Neuromuscular Disease (NMD) and Chest wall disorders.

Obstructive Sleep Apnea (OSA), a form of Sleep Disordered Breathing(SDB), is characterised by events including occlusion or obstruction ofthe upper air passage during sleep. It results from a combination of anabnormally small upper airway and the normal loss of muscle tone in theregion of the tongue, soft palate and posterior oropharyngeal wallduring sleep. The condition causes the affected patient to stopbreathing for periods typically of 30 to 120 seconds in duration,sometimes 200 to 300 times per night. It often causes excessive daytimesomnolence, and it may cause cardiovascular disease and brain damage.The syndrome is a common disorder, particularly in middle agedoverweight males, although a person affected may have no awareness ofthe problem. See U.S. Pat. No. 4,944,310 (Sullivan).

Cheyne-Stokes Respiration (CSR) is another form of sleep disorderedbreathing. CSR is a disorder of a patient's respiratory controller inwhich there are rhythmic alternating periods of waxing and waningventilation known as CSR cycles. CSR is characterised by repetitivede-oxygenation and re-oxygenation of the arterial blood. It is possiblethat CSR is harmful because of the repetitive hypoxia. In some patientsCSR is associated with repetitive arousal from sleep, which causessevere sleep disruption, increased sympathetic activity, and increasedafterload. See U.S. Pat. No. 6,532,959 (Berthon-Jones).

Respiratory failure is an umbrella term for respiratory disorders inwhich the lungs are unable to inspire sufficient oxygen or exhalesufficient CO₂ to meet the patient's needs. Respiratory failure mayencompass some or all of the following disorders.

A patient with respiratory insufficiency (a form of respiratory failure)may experience abnormal shortness of breath on exercise.

Obesity Hyperventilation Syndrome (OHS) is defined as the combination ofsevere obesity and awake chronic hypercapnia, in the absence of otherknown causes for hypoventilation. Symptoms include dyspnea, morningheadache and excessive daytime sleepiness.

Chronic Obstructive Pulmonary Disease (COPD) encompasses any of a groupof lower airway diseases that have certain characteristics in common.These include increased resistance to air movement, extended expiratoryphase of respiration, and loss of the normal elasticity of the lung.Examples of COPD are emphysema and chronic bronchitis. COPD is caused bychronic tobacco smoking (primary risk factor), occupational exposures,air pollution and genetic factors. Symptoms include: dyspnea onexertion, chronic cough and sputum production.

Neuromuscular Disease (NMD) is a broad term that encompasses manydiseases and ailments that impair the functioning of the muscles eitherdirectly via intrinsic muscle pathology, or indirectly via nervepathology. Some NMD patients are characterised by progressive muscularimpairment leading to loss of ambulation, being wheelchair-bound,swallowing difficulties, respiratory muscle weakness and, eventually,death from respiratory failure. Neuromuscular disorders can be dividedinto rapidly progressive and slowly progressive: (i) Rapidly progressivedisorders: Characterised by muscle impairment that worsens over monthsand results in death within a few years (e.g. Amyotrophic lateralsclerosis (ALS) and Duchenne muscular dystrophy (DMD) in teenagers);(ii) Variable or slowly progressive disorders: Characterised by muscleimpairment that worsens over years and only mildly reduces lifeexpectancy (e.g. Limb girdle, Facioscapulohumeral and Myotonic musculardystrophy). Symptoms of respiratory failure in NMD include: increasinggeneralised weakness, dysphagia, dyspnea on exertion and at rest,fatigue, sleepiness, morning headache, and difficulties withconcentration and mood changes.

Chest wall disorders are a group of thoracic deformities that result ininefficient coupling between the respiratory muscles and the thoraciccage. The disorders are usually characterised by a restrictive defectand share the potential of long term hypercapnic respiratory failure.Scoliosis and/or kyphoscoliosis may cause severe respiratory failure.Symptoms of respiratory failure include: dyspnea on exertion, peripheraloedema, orthopnea, repeated chest infections, morning headaches,fatigue, poor sleep quality and loss of appetite.

A range of therapies have been used to treat or ameliorate suchconditions. Furthermore, otherwise healthy individuals may takeadvantage of such therapies to prevent respiratory disorders fromarising. However, these have a number of shortcomings.

1.2.2 Therapy

Various therapies, such as Continuous Positive Airway Pressure (CPAP)therapy, Non-invasive ventilation (NIV) and Invasive ventilation (IV)have been used to treat one or more of the above respiratory disorders.

Continuous Positive Airway Pressure (CPAP) therapy has been used totreat Obstructive Sleep Apnea (OSA). The mechanism of action is thatcontinuous positive airway pressure acts as a pneumatic splint and mayprevent upper airway occlusion, such as by pushing the soft palate andtongue forward and away from the posterior oropharyngeal wall. Treatmentof OSA by CPAP therapy may be voluntary, and hence patients may electnot to comply with therapy if they find devices used to provide suchtherapy one or more of: uncomfortable, difficult to use, expensive andaesthetically unappealing.

Non-invasive ventilation (NIV) provides ventilatory support to a patientthrough the upper airways to assist the patient breathing and/ormaintain adequate oxygen levels in the body by doing some or all of thework of breathing. The ventilatory support is provided via anon-invasive patient interface. NIV has been used to treat CSR andrespiratory failure, in forms such as OHS, COPD, NMD and Chest Walldisorders. In some forms, the comfort and effectiveness of thesetherapies may be improved.

Invasive ventilation (IV) provides ventilatory support to patients thatare no longer able to effectively breathe themselves and may be providedusing a tracheostomy tube. In some forms, the comfort and effectivenessof these therapies may be improved.

1.2.3 Treatment Systems

These therapies may be provided by a treatment system or device. Suchsystems and devices may also be used to diagnose a condition withouttreating it.

A treatment system may comprise a Respiratory Pressure Therapy Device(RPT device), an air circuit, a humidifier, a patient interface, anddata management.

Another form of treatment system is a mandibular repositioning device.

1.2.3.1 Patient Interface

A patient interface may be used to interface respiratory equipment toits wearer, for example by providing a flow of air to an entrance to theairways. The flow of air may be provided via a mask to the nose and/ormouth, a tube to the mouth or a tracheostomy tube to the trachea of apatient. Depending upon the therapy to be applied, the patient interfacemay form a seal, e.g., with a region of the patient's face, tofacilitate the delivery of gas at a pressure at sufficient variance withambient pressure to effect therapy, e.g., at a positive pressure ofabout 10 cmH₂O relative to ambient pressure. For other forms of therapy,such as the delivery of oxygen, the patient interface may not include aseal sufficient to facilitate delivery to the airways of a supply of gasat a positive pressure of about 10 cmH₂O.

Certain other mask systems may be functionally unsuitable for thepresent field. For example, purely ornamental masks may be unable tomaintain a suitable pressure. Mask systems used for underwater swimmingor diving may be configured to guard against ingress of water from anexternal higher pressure, but not to maintain air internally at a higherpressure than ambient.

Certain masks may be clinically unfavourable for the present technologye.g. if they block airflow via the nose and only allow it via the mouth.

Certain masks may be uncomfortable or impractical for the presenttechnology if they require a patient to insert a portion of a maskstructure in their mouth to create and maintain a seal via their lips.

Certain masks may be impractical for use while sleeping, e.g. forsleeping while lying on one's side in bed with a head on a pillow.

The design of a patient interface presents a number of challenges. Theface has a complex three-dimensional shape. The size and shape of nosesand heads varies considerably between individuals. Since the headincludes bone, cartilage and soft tissue, different regions of the facerespond differently to mechanical forces. The jaw or mandible may moverelative to other bones of the skull. The whole head may move during thecourse of a period of respiratory therapy.

As a consequence of these challenges, some masks suffer from being oneor more of obtrusive, aesthetically undesirable, costly, poorly fitting,difficult to use, and uncomfortable especially when worn for longperiods of time or when a patient is unfamiliar with a system. Wronglysized masks can give rise to reduced compliance, reduced comfort andpoorer patient outcomes. Masks designed solely for aviators, masksdesigned as part of personal protection equipment (e.g. filter masks),SCUBA masks, or for the administration of anaesthetics may be tolerablefor their original application, but nevertheless such masks may beundesirably uncomfortable to be worn for extended periods of time, e.g.,several hours. This discomfort may lead to a reduction in patientcompliance with therapy. This is even more so if the mask is to be wornduring sleep.

CPAP therapy is highly effective to treat certain respiratory disorders,provided patients comply with therapy. If a mask is uncomfortable, ordifficult to use a patient may not comply with therapy. Since it isoften recommended that a patient regularly wash their mask, if a mask isdifficult to clean (e.g., difficult to assemble or disassemble),patients may not clean their mask and this may impact on patientcompliance.

While a mask for other applications (e.g. aviators) may not be suitablefor use in treating sleep disordered breathing, a mask designed for usein treating sleep disordered breathing may be suitable for otherapplications.

For these reasons, patient interfaces for delivery of CPAP during sleepform a distinct field.

1.2.3.1.1 Seal-Forming Structure

Patient interfaces may include a seal-forming structure. Since it is indirect contact with the patient's face, the shape and configuration ofthe seal-forming structure can have a direct impact the effectivenessand comfort of the patient interface.

A patient interface may be partly characterised according to the designintent of where the seal-forming structure is to engage with the face inuse. In one form of patient interface, a seal-forming structure maycomprise a first sub-portion to form a seal around the left naris and asecond sub-portion to form a seal around the right naris. In one form ofpatient interface, a seal-forming structure may comprise a singleelement that surrounds both nares in use. Such single element may bedesigned to for example overlay an upper lip region and a nasal bridgeregion of a face. In one form of patient interface a seal-formingstructure may comprise an element that surrounds a mouth region in use,e.g. by forming a seal on a lower lip region of a face. In one form ofpatient interface, a seal-forming structure may comprise a singleelement that surrounds both nares and a mouth region in use. Thesedifferent types of patient interfaces may be known by a variety of namesby their manufacturer including nasal masks, full-face masks, nasalpillows, nasal puffs and oro-nasal masks.

A seal-forming structure that may be effective in one region of apatient's face may be inappropriate in another region, e.g. because ofthe different shape, structure, variability and sensitivity regions ofthe patient's face. For example, a seal on swimming goggles thatoverlays a patient's forehead may not be appropriate to use on apatient's nose.

Certain seal-forming structures may be designed for mass manufacturesuch that one design fit and be comfortable and effective for a widerange of different face shapes and sizes. To the extent to which thereis a mismatch between the shape of the patient's face, and theseal-forming structure of the mass-manufactured patient interface, oneor both must adapt in order for a seal to form.

One type of seal-forming structure extends around the periphery of thepatient interface, and is intended to seal against the patient's facewhen force is applied to the patient interface with the seal-formingstructure in confronting engagement with the patient's face. Theseal-forming structure may include an air or fluid filled cushion, or amoulded or formed surface of a resilient seal element made of anelastomer such as a rubber. With this type of seal-forming structure, ifthe fit is not adequate, there will be gaps between the seal-formingstructure and the face, and additional force will be required to forcethe patient interface against the face in order to achieve a seal.

Another type of seal-forming structure incorporates a flap seal of thinmaterial positioned about the periphery of the mask so as to provide aself-sealing action against the face of the patient when positivepressure is applied within the mask. Like the previous style of sealforming portion, if the match between the face and the mask is not good,additional force may be required to achieve a seal, or the mask mayleak. Furthermore, if the shape of the seal-forming structure does notmatch that of the patient, it may crease or buckle in use, giving riseto leaks.

Another type of seal-forming structure may comprise a friction-fitelement, e.g. for insertion into a naris, however some patients findthese uncomfortable.

Another form of seal-forming structure may use adhesive to achieve aseal. Some patients may find it inconvenient to constantly apply andremove an adhesive to their face.

A range of patient interface seal-forming structure technologies aredisclosed in the following patent applications, assigned to ResMedLimited: WO 1998/004,310; WO 2006/074,513; WO 2010/135,785.

One form of nasal pillow is found in the Adam Circuit manufactured byPuritan Bennett. Another nasal pillow, or nasal puff is the subject ofU.S. Pat. No. 4,782,832 (Trimble et al.), assigned to Puritan-BennettCorporation.

ResMed Limited has manufactured the following products that incorporatenasal pillows: SWIFT™ nasal pillows mask, SWIFT™ II nasal pillows mask,SWIFT™ LT nasal pillows mask, SWIFT™ FX nasal pillows mask and MIRAGELIBERTY™ full-face mask. The following patent applications, assigned toResMed Limited, describe examples of nasal pillows masks: InternationalPatent Application WO2004/073,778 (describing amongst other thingsaspects of the ResMed Limited SWIFT™ nasal pillows), US PatentApplication 2009/0044808 (describing amongst other things aspects of theResMed Limited SWIFT™ LT nasal pillows); International PatentApplications WO 2005/063,328 and WO 2006/130,903 (describing amongstother things aspects of the ResMed Limited MIRAGE LIBERTY™ full-facemask); International Patent Application WO 2009/052,560 (describingamongst other things aspects of the ResMed Limited SWIFT™ FX nasalpillows).

1.2.3.1.2 Positioning and Stabilising

A seal-forming structure of a patient interface used for positive airpressure therapy is subject to the corresponding force of the airpressure to disrupt a seal. Thus a variety of techniques have been usedto position the seal-forming structure, and to maintain it in sealingrelation with the appropriate portion of the face.

One technique is the use of adhesives. See for example US PatentApplication Publication No. US 2010/0000534. However, the use ofadhesives may be uncomfortable for some.

Another technique is the use of one or more straps and/or stabilisingharnesses. Many such harnesses suffer from being one or more ofill-fitting, bulky, uncomfortable and awkward to use.

1.2.3.2 Respiratory Pressure Therapy (RPT) Device

A respiratory pressure therapy (RPT) device may be used to deliver oneor more of a number of therapies described above, such as by generatinga flow of air for delivery to an entrance to the airways. The flow ofair may be pressurised. Examples of RPT devices include a CPAP deviceand a ventilator.

Air pressure generators are known in a range of applications, e.g.industrial-scale ventilation systems. However, air pressure generatorsfor medical applications have particular requirements not fulfilled bymore generalised air pressure generators, such as the reliability, sizeand weight requirements of medical devices. In addition, even devicesdesigned for medical treatment may suffer from shortcomings, pertainingto one or more of: comfort, noise, ease of use, efficacy, size, weight,manufacturability, cost, and reliability.

An example of the special requirements of certain RPT devices isacoustic noise.

Table of noise output levels of prior RPT devices (one specimen only,measured using test method specified in ISO 3744 in CPAP mode at 10 cmH₂O). A-weighted sound Year RPT Device name pressure level dB(A)(approx.) C-Series Tango ™ 31.9 2007 C-Series Tango ™ with Humidifier33.1 2007 S8 Escape ™ II 30.5 2005 S8 Escape ™ II with H4i ™ Humidifier31.1 2005 S9 AutoSet ™ 26.5 2010 S9 AutoSet ™ with H5i Humidifier 28.62010

One known RPT device used for treating sleep disordered breathing is theS9 Sleep Therapy System, manufactured by ResMed Limited. Another exampleof an RPT device is a ventilator. Ventilators such as the ResMedStellar™ Series of Adult and Paediatric Ventilators may provide supportfor invasive and non-invasive non-dependent ventilation for a range ofpatients for treating a number of conditions such as but not limited toNMD, OHS and COPD.

The ResMed Elisée™ 150 ventilator and ResMed VS III™ ventilator mayprovide support for invasive and non-invasive dependent ventilationsuitable for adult or paediatric patients for treating a number ofconditions. These ventilators provide volumetric and barometricventilation modes with a single or double limb circuit. RPT devicestypically comprise a pressure generator, such as a motor-driven bloweror a compressed gas reservoir, and are configured to supply a flow ofair to the airway of a patient. In some cases, the flow of air may besupplied to the airway of the patient at positive pressure. The outletof the RPT device is connected via an air circuit to a patient interfacesuch as those described above.

The designer of a device may be presented with an infinite number ofchoices to make. Design criteria often conflict, meaning that certaindesign choices are far from routine or inevitable. Furthermore, thecomfort and efficacy of certain aspects may be highly sensitive tosmall, subtle changes in one or more parameters.

1.2.3.3 Humidifier

Delivery of a flow of air without humidification may cause drying ofairways. The use of a humidifier with an RPT device and the patientinterface produces humidified gas that minimizes drying of the nasalmucosa and increases patient airway comfort. In addition in coolerclimates, warm air applied generally to the face area in and about thepatient interface is more comfortable than cold air.

A range of artificial humidification devices and systems are known,however they may not fulfil the specialised requirements of a medicalhumidifier.

Medical humidifiers are used to increase humidity and/or temperature ofthe flow of air in relation to ambient air when required, typicallywhere the patient may be asleep or resting (e.g. at a hospital). Amedical humidifier for bedside placement may be small. A medicalhumidifier may be configured to only humidify and/or heat the flow ofair delivered to the patient without humidifying and/or heating thepatient's surroundings. Room-based systems (e.g. a sauna, an airconditioner, or an evaporative cooler), for example, may also humidifyair that is breathed in by the patient, however those systems would alsohumidify and/or heat the entire room, which may cause discomfort to theoccupants. Furthermore medical humidifiers may have more stringentsafety constraints than industrial humidifiers

While a number of medical humidifiers are known, they can suffer fromone or more shortcomings. Some medical humidifiers may provideinadequate humidification, some are difficult or inconvenient to use bypatients.

1.2.3.4 Vent Technologies

Some forms of treatment systems may include a vent to allow the washoutof exhaled carbon dioxide. The vent may allow a flow of gas from aninterior space of a patient interface, e.g., the plenum chamber, to anexterior of the patient interface, e.g., to ambient.

The vent may comprise an orifice and gas may flow through the orifice inuse of the mask. Many such vents are noisy. Others may become blocked inuse and thus provide insufficient washout. Some vents may be disruptiveof the sleep of a bed partner 1100 of the patient 1000, e.g. throughnoise or focused airflow.

ResMed Limited has developed a number of improved mask venttechnologies. See International Patent Application Publication No. WO1998/034,665; International Patent Application Publication No. WO2000/078,381; U.S. Pat. No. 6,581,594; US Patent Application PublicationNo. US 2009/0050156; US Patent Application Publication No. 2009/0044808.

Table of noise of prior masks (ISO 17510-2:2007, 10 cm H₂O pressure at 1m) A-weighted A-weighted sound sound power pressure level dB(A) dB(A)Year Mask name Mask type (uncertainty) (uncertainty) (approx.)Glue-on(*) nasal 50.9 42.9 1981 ResCare nasal 31.5 23.5 1993 standard(*)ResMed nasal 29.5 21.5 1998 Mirage ™(*) ResMed nasal 36 (3) 28 (3) 2000UltraMirage ™ ResMed nasal 32 (3) 24 (3) 2002 Mirage Activa ™ ResMednasal 30 (3) 22 (3) 2008 Mirage Micro ™ ResMed nasal 29 (3) 22 (3) 2008Mirage ™ SoftGel ResMed nasal 26 (3) 18 (3) 2010 Mirage ™ FX ResMednasal 37   29   2004 Mirage Swift ™(*) pillows ResMed nasal 28 (3) 20(3) 2005 Mirage Swift ™ pillows II ResMed nasal 25 (3) 17 (3) 2008Mirage Swift ™ pillows LT ResMed AirFit nasal 21 (3) 13 (3) 2014 P10pillows (*one specimen only, measured using test method specified in ISO3744 in CPAP mode at 10 cmH₂O)

Sound pressure values of a variety of objects are listed below

A-weighted Object sound pressure dB(A) Notes Vacuum cleaner: Nilfisk 68ISO 3744 at 1 m Walter Broadly Litter Hog: distance B+ GradeConversational speech 60 1 m distance Average home 50 Quiet library 40Quiet bedroom at night 30 Background in TV studio 20

2 BRIEF SUMMARY OF THE TECHNOLOGY

The present technology is directed towards providing medical devicesused in the diagnosis, amelioration, treatment, or prevention ofrespiratory disorders having one or more of improved comfort, cost,efficacy, ease of use and manufacturability.

A first aspect of the present technology relates to apparatus used inthe diagnosis, amelioration, treatment or prevention of a respiratorydisorder.

Another aspect of the present technology relates to methods used in thediagnosis, amelioration, treatment or prevention of a respiratorydisorder.

An aspect of certain forms of the present technology is to providemethods and/or apparatus that improve the compliance of patients withrespiratory therapy.

An aspect of the present technology includes a gas washout vent for apatient interface system, the gas washout vent comprising: a housingcomprising a first wall with one or more passages through the firstwall, the one or more passages being configured to provide fluidcommunication with a portion of the patient interface system that isconfigured to be exposed to the therapy pressure, the housing at leastpartially defining a second opening that is in communication withambient atmosphere; and a diffusing material located at least partiallywithin the housing.

An aspect of the present technology includes a gas washout vent for apatient interface system configured to maintain a therapy pressure in arange of about 4 cmH2O to about 30 cmH2O above ambient air pressure inuse, throughout a patient's respiratory cycle, while the patient issleeping, to ameliorate a respiratory or a sleep disordered breathingcondition, the gas washout vent comprising: a housing comprising a firstwall with one or more passages through the first wall, the one or morepassages being configured to provide fluid communication with a portionof the patient interface system that is configured to be exposed to thetherapy pressure, the passages including respective first openings on afirst surface of the first wall, the housing at least partially defininga second opening that is in communication with ambient atmosphere; and adiffusing material located at least partially within the housing to beadjacent the first surface, a surface of the diffusing material facingthe first surface being spaced away from the first surface by a gap thatextends to provide a fluid communication between all of the firstopenings, as well as between all of the first openings and the secondopening; wherein the housing is configured so that air is prevented fromflowing out of the housing at all areas directly opposite each of thefirst openings.

In examples, (a) the housing further comprises a third opening incommunication with ambient atmosphere, wherein the third opening doesnot overlap with an area of an outlet of any of the passages that isprojected along a central axis of the respective passages, and islocated so that at least part of the diffusing material is between eachfirst opening and the third opening; (b) the third opening is orientedso that a central axis through the third opening is angled with respectto the central axis of any of the passages; (c) the third opening issized so that completely blocking the third opening does notsubstantially decrease the air flow through the gas washout vent whenthe portion of the patient interface is exposed to the therapy pressure;(d) the air flow through the gas washout vent does not decrease by morethan three percent; (e) the third opening is one of a plurality of thirdopenings; (f) the third opening is configured for water removal; (g) thesecond opening comprises a plurality of second openings; (h) at leastone of the one or more passages is sized so that at least a portion ofair exiting the respective first opening penetrates into the diffusingmaterial when the portion of the patient interface is exposed to thetherapy pressure; (i) the gas washout vent is configured so that theportion of the air penetrating the diffusing material exits thediffusing material and re-enters the gap before flowing out of thesecond opening; (j) the gas washout vent is configured so that theportion of the air exiting the respective first opening penetrates andexits the diffusing material via the surface; (k) no more than 28 dB(A)noise is generated when air exits the second opening as a result of theportion of the patient interface being exposed to the therapy pressure;(l) the diffusing material comprises uncompressed fibers; (m) thediffusing material comprises moisture wicking material; (n) the moisturewicking material is sintered plastic; (o) the diffusing materialcomprises hydrophobic material; (p) the diffusing material possessesantibacterial properties; (q) the first wall is fixed in the housing ina non-releasable manner; (r) the gap is at least partially bounded bythe first wall from the first openings to the second opening; (s) thegap is formed by the surface from a location opposed to the firstopenings to a portion of the diffusing material that is closest to thesecond opening; (t) the gap is tapered in a radial direction; (u) thegap tapers off in a radially outward direction; (v) the surface of thediffusing material and the first surface are parallel; (x) the surfaceof the diffusing material and the first surface are inclined withrespect to one another; (z) a portion of the housing is removable toallow replacement of the diffusing material; (aa) the second opening andthe gap are sized so that a majority of pressure drop during the flow ofair through the passages, the gap and the second opening, occurs priorto exiting the passages; and/or (bb) the gas washout vent comprises aseparate apparatus arranged for engaging with a patient interface or anair circuit.

Another aspect of the present technology includes a system for treatinga respiratory disorder in a patient that comprises a respiratorypressure therapy device; a humidifier; an air circuit; and a patientinterface, and at least one of the air circuit and the patient interfacecomprises the gas washout vent according to any preceding aspect orexample.

Of course, portions of the aspects may form sub-aspects of the presenttechnology. Also, various ones of the sub-aspects and/or aspects may becombined in various manners and also constitute additional aspects orsub-aspects of the present technology.

Other features of the technology will be apparent from consideration ofthe information contained in the following detailed description,abstract, drawings and claims.

3 BRIEF DESCRIPTION OF THE DRAWINGS

The present technology is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings, in whichlike reference numerals refer to similar elements including:

3.1 Treatment Systems

FIG. 1A shows a system including a patient 1000 wearing a patientinterface 3000, in the form of nasal pillows, receiving a supply of airat positive pressure from an RPT device 4000. Air from the RPT device4000 is humidified in a humidifier 5000, and passes along an air circuit4170 to the patient 1000. A bed partner 1100 is also shown. The patientis sleeping in a supine sleeping position.

FIG. 1B shows a system including a patient 1000 wearing a patientinterface 3000, in the form of a nasal mask, receiving a supply of airat positive pressure from an RPT device 4000. Air from the RPT device ishumidified in a humidifier 5000, and passes along an air circuit 4170 tothe patient 1000.

FIG. 1C shows a system including a patient 1000 wearing a patientinterface 3000, in the form of a full-face mask, receiving a supply ofair at positive pressure from an RPT device 4000. Air from the RPTdevice is humidified in a humidifier 5000, and passes along an aircircuit 4170 to the patient 1000. The patient is sleeping in a sidesleeping position.

3.2 Respiratory System and Facial Anatomy

FIG. 2A shows an overview of a human respiratory system including thenasal and oral cavities, the larynx, vocal folds, oesophagus, trachea,bronchus, lung, alveolar sacs, heart and diaphragm.

FIG. 2B shows a view of a human upper airway including the nasal cavity,nasal bone, lateral nasal cartilage, greater alar cartilage, nostril,lip superior, lip inferior, larynx, hard palate, soft palate,oropharynx, tongue, epiglottis, vocal folds, oesophagus and trachea.

FIG. 2C is a front view of a face with several features of surfaceanatomy identified including the lip superior, upper vermilion, lowervermilion, lip inferior, mouth width, endocanthion, a nasal ala,nasolabial sulcus and cheilion. Also indicated are the directionssuperior, inferior, radially inward and radially outward.

FIG. 2D is a side view of a head with several features of surfaceanatomy identified including glabella, sellion, pronasale, subnasale,lip superior, lip inferior, supramenton, nasal ridge, alar crest point,otobasion superior and otobasion inferior. Also indicated are thedirections superior & inferior, and anterior & posterior.

FIG. 2E is a further side view of a head. The approximate locations ofthe Frankfort horizontal and nasolabial angle are indicated. The coronalplane is also indicated.

FIG. 2F shows a base view of a nose with several features identifiedincluding naso-labial sulcus, lip inferior, upper Vermilion, naris,subnasale, columella, pronasale, the major axis of a naris and thesagittal plane.

FIG. 2G shows a side view of the superficial features of a nose.

FIG. 2H shows subcutaneal structures of the nose, including lateralcartilage, septum cartilage, greater alar cartilage, lesser alarcartilage, sesamoid cartilage, nasal bone, epidermis, adipose tissue,frontal process of the maxilla and fibrofatty tissue.

FIG. 2I shows a medial dissection of a nose, approximately severalmillimeters from a sagittal plane, amongst other things showing theseptum cartilage and medial crus of greater alar cartilage.

FIG. 2J shows a front view of the bones of a skull including thefrontal, nasal and zygomatic bones. Nasal concha are indicated, as arethe maxilla, and mandible.

FIG. 2K shows a lateral view of a skull with the outline of the surfaceof a head, as well as several muscles. The following bones are shown:frontal, sphenoid, nasal, zygomatic, maxilla, mandible, parietal,temporal and occipital. The mental protuberance is indicated. Thefollowing muscles are shown: digastricus, masseter, sternocleidomastoidand trapezius.

FIG. 2L shows an anterolateral view of a nose.

3.3 Patient Interface

FIG. 3A shows a patient interface in the form of a nasal mask inaccordance with one form of the present technology.

FIG. 3B shows a schematic of a cross-section through a structure at apoint. An outward normal at the point is indicated. The curvature at thepoint has a positive sign, and a relatively large magnitude whencompared to the magnitude of the curvature shown in FIG. 3C.

FIG. 3C shows a schematic of a cross-section through a structure at apoint. An outward normal at the point is indicated. The curvature at thepoint has a positive sign, and a relatively small magnitude whencompared to the magnitude of the curvature shown in FIG. 3B.

FIG. 3D shows a schematic of a cross-section through a structure at apoint. An outward normal at the point is indicated. The curvature at thepoint has a value of zero.

FIG. 3E shows a schematic of a cross-section through a structure at apoint. An outward normal at the point is indicated. The curvature at thepoint has a negative sign, and a relatively small magnitude whencompared to the magnitude of the curvature shown in FIG. 3F.

FIG. 3F shows a schematic of a cross-section through a structure at apoint. An outward normal at the point is indicated. The curvature at thepoint has a negative sign, and a relatively large magnitude whencompared to the magnitude of the curvature shown in FIG. 3E.

FIG. 3G shows a cushion for a mask that includes two pillows. Anexterior surface of the cushion is indicated. An edge of the surface isindicated. Dome and saddle regions are indicated.

FIG. 3H shows a cushion for a mask. An exterior surface of the cushionis indicated. An edge of the surface is indicated. A path on the surfacebetween points A and B is indicated. A straight line distance between Aand B is indicated. Two saddle regions and a dome region are indicated.

FIG. 3I shows the surface of a structure, with a one dimensional hole inthe surface. The illustrated plane curve forms the boundary of a onedimensional hole.

FIG. 3J shows a cross-section through the structure of FIG. 3I. Theillustrated surface bounds a two dimensional hole in the structure ofFIG. 3I.

FIG. 3K shows a perspective view of the structure of FIG. 3I, includingthe two dimensional hole and the one dimensional hole. Also shown is thesurface that bounds a two dimensional hole in the structure of FIG. 3I.

FIG. 3L shows a mask having an inflatable bladder as a cushion.

FIG. 3M shows a cross-section through the mask of FIG. 3L, and shows theinterior surface of the bladder. The interior surface bounds the twodimensional hole in the mask.

FIG. 3N shows a further cross-section through the mask of FIG. 3L. Theinterior surface is also indicated.

FIG. 3O illustrates a left-hand rule.

FIG. 3P illustrates a right-hand rule.

FIG. 3Q shows a left ear, including the left ear helix.

FIG. 3R shows a right ear, including the right ear helix.

FIG. 3S shows a right-hand helix.

FIG. 3T shows a view of a mask, including the sign of the torsion of thespace curve defined by the edge of the sealing membrane in differentregions of the mask.

3.4 Vent

FIG. 4A shows a vent in accordance with one form of the presenttechnology.

FIG. 4B show a vent in accordance with another form of the presenttechnology.

FIG. 4C show a vent in accordance with another form of the presenttechnology.

FIG. 4D show a vent in accordance with another form of the presenttechnology.

FIG. 4E show a vent in accordance with another form of the presenttechnology.

FIG. 4F show a vent in accordance with another form of the presenttechnology.

FIG. 4G show a vent in accordance with another form of the presenttechnology.

FIG. 4H show the vent of FIG. 4G with a top portion removed so thatinterior structure is visible.

FIG. 4I show a cross-section of FIG. 4H but with the top portionincluded.

FIG. 4J show a first alternative cross-section of FIG. 4H with anadditional component included.

FIG. 4K show a second alternative cross-section of FIG. 4H with analternative version of the additional component included.

4 DETAILED DESCRIPTION OF EXAMPLES OF THE TECHNOLOGY

Before the present technology is described in further detail, it is tobe understood that the technology is not limited to the particularexamples described herein, which may vary. It is also to be understoodthat the terminology used in this disclosure is for the purpose ofdescribing only the particular examples discussed herein, and is notintended to be limiting.

The following description is provided in relation to various exampleswhich may share one or more common characteristics and/or features. Itis to be understood that one or more features of any one example may becombinable with one or more features of another example or otherexamples. In addition, any single feature or combination of features inany of the examples may constitute a further example.

4.1 Therapy

In one form, the present technology comprises a method for treating arespiratory disorder comprising the step of applying positive pressureto the entrance of the airways of a patient 1000.

In certain examples of the present technology, a supply of air atpositive pressure is provided to the nasal passages of the patient viaone or both nares.

In certain examples of the present technology, mouth breathing islimited, restricted or prevented.

4.2 Treatment Systems

In one form, the present technology comprises an apparatus or device fortreating a respiratory disorder. The apparatus or device may comprise anRPT device 4000 for supplying pressurised air to the patient 1000 via anair circuit 4170 to a patient interface 3000.

4.3 Patient Interface

A non-invasive patient interface 3000 in accordance with one aspect ofthe present technology comprises the following functional aspects: aseal-forming structure 3100, a plenum chamber 3200, a positioning andstabilising structure 3300, a vent 3400, one form of connection port3600 for connection to air circuit 4170, and a forehead support 3700. Insome forms a functional aspect may be provided by one or more physicalcomponents. In some forms, one physical component may provide one ormore functional aspects. In use the seal-forming structure 3100 isarranged to surround an entrance to the airways of the patient so as tofacilitate the supply of air at positive pressure to the airways.

If a patient interface is unable to comfortably deliver a minimum levelof positive pressure to the airways, the patient interface may beunsuitable for respiratory pressure therapy.

The patient interface 3000 in accordance with one form of the presenttechnology is constructed and arranged to be able to provide a supply ofair at a positive pressure of at least 6 cmH₂O with respect to ambient.

The patient interface 3000 in accordance with one form of the presenttechnology is constructed and arranged to be able to provide a supply ofair at a positive pressure of at least 10 cmH₂O with respect to ambient.

The patient interface 3000 in accordance with one form of the presenttechnology is constructed and arranged to be able to provide a supply ofair at a positive pressure of at least 20 cmH₂O with respect to ambient.

4.3.1 Seal-Forming Structure

In one form of the present technology, a seal-forming structure 3100provides a target seal-forming region, and may additionally provide acushioning function. The target seal-forming region is a region on theseal-forming structure 3100 where sealing may occur. The region wheresealing actually occurs—the actual sealing surface—may change within agiven treatment session, from day to day, and from patient to patient,depending on a range of factors including for example, where the patientinterface was placed on the face, tension in the positioning andstabilising structure and the shape of a patient's face.

In one form the target seal-forming region is located on an outsidesurface of the seal-forming structure 3100.

In certain forms of the present technology, the seal-forming structure3100 is constructed from a biocompatible material, e.g. silicone rubber.

A seal-forming structure 3100 in accordance with the present technologymay be constructed from a soft, flexible, resilient material such assilicone.

In certain forms of the present technology, a system is providedcomprising more than one a seal-forming structure 3100, each beingconfigured to correspond to a different size and/or shape range. Forexample the system may comprise one form of a seal-forming structure3100 suitable for a large sized head, but not a small sized head andanother suitable for a small sized head, but not a large sized head.

4.3.1.1 Sealing Mechanisms

In one form, the seal-forming structure includes a sealing flangeutilizing a pressure assisted sealing mechanism. In use, the sealingflange can readily respond to a system positive pressure in the interiorof the plenum chamber 3200 acting on its underside to urge it into tightsealing engagement with the face. The pressure assisted mechanism mayact in conjunction with elastic tension in the positioning andstabilising structure.

In one form, the seal-forming structure 3100 comprises a sealing flangeand a support flange. The sealing flange comprises a relatively thinmember with a thickness of less than about 1 mm, for example about 0.25mm to about 0.45 mm, which extends around the perimeter of the plenumchamber 3200. Support flange may be relatively thicker than the sealingflange. The support flange is disposed between the sealing flange andthe marginal edge of the plenum chamber 3200, and extends at least partof the way around the perimeter. The support flange is or includes aspring-like element and functions to support the sealing flange frombuckling in use.

In one form, the seal-forming structure may comprise a compressionsealing portion or a gasket sealing portion. In use the compressionsealing portion, or the gasket sealing portion is constructed andarranged to be in compression, e.g. as a result of elastic tension inthe positioning and stabilising structure.

In one form, the seal-forming structure comprises a tension portion. Inuse, the tension portion is held in tension, e.g. by adjacent regions ofthe sealing flange.

In one form, the seal-forming structure comprises a region having atacky or adhesive surface.

In certain forms of the present technology, a seal-forming structure maycomprise one or more of a pressure-assisted sealing flange, acompression sealing portion, a gasket sealing portion, a tensionportion, and a portion having a tacky or adhesive surface.

4.3.1.2 Nose Bridge or Nose Ridge Region

In one form, the non-invasive patient interface 3000 comprises aseal-forming structure that forms a seal in use on a nose bridge regionor on a nose-ridge region of the patient's face.

In one form, the seal-forming structure includes a saddle-shaped regionconstructed to form a seal in use on a nose bridge region or on anose-ridge region of the patient's face.

4.3.1.3 Upper Lip Region

In one form, the non-invasive patient interface 3000 comprises aseal-forming structure that forms a seal in use on an upper lip region(that is, the lip superior) of the patient's face.

In one form, the seal-forming structure includes a saddle-shaped regionconstructed to form a seal in use on an upper lip region of thepatient's face.

4.3.1.4 Chin-Region

In one form the non-invasive patient interface 3000 comprises aseal-forming structure that forms a seal in use on a chin-region of thepatient's face.

In one form, the seal-forming structure includes a saddle-shaped regionconstructed to form a seal in use on a chin-region of the patient'sface.

4.3.1.5 Forehead Region

In one form, the seal-forming structure that forms a seal in use on aforehead region of the patient's face. In such a form, the plenumchamber may cover the eyes in use.

4.3.1.6 Nasal Pillows

In one form the seal-forming structure of the non-invasive patientinterface 3000 comprises a pair of nasal puffs, or nasal pillows, eachnasal puff or nasal pillow being constructed and arranged to form a sealwith a respective naris of the nose of a patient.

Nasal pillows in accordance with an aspect of the present technologyinclude: a frusto-cone, at least a portion of which forms a seal on anunderside of the patient's nose, a stalk, a flexible region on theunderside of the frusto-cone and connecting the frusto-cone to thestalk. In addition, the structure to which the nasal pillow of thepresent technology is connected includes a flexible region adjacent thebase of the stalk. The flexible regions can act in concert to facilitatea universal joint structure that is accommodating of relative movementboth displacement and angular of the frusto-cone and the structure towhich the nasal pillow is connected. For example, the frusto-cone may beaxially displaced towards the structure to which the stalk is connected.

4.3.2 Plenum Chamber

The plenum chamber 3200 has a perimeter that is shaped to becomplementary to the surface contour of the face of an average person inthe region where a seal will form in use. In use, a marginal edge of theplenum chamber 3200 is positioned in close proximity to an adjacentsurface of the face. Actual contact with the face is provided by theseal-forming structure 3100. The seal-forming structure 3100 may extendin use about the entire perimeter of the plenum chamber 3200. In someforms, the plenum chamber 3200 and the seal-forming structure 3100 areformed from a single homogeneous piece of material.

In certain forms of the present technology, the plenum chamber 3200 doesnot cover the eyes of the patient in use. In other words, the eyes areoutside the pressurised volume defined by the plenum chamber. Such formstend to be less obtrusive and/or more comfortable for the wearer, whichcan improve compliance with therapy.

In certain forms of the present technology, the plenum chamber 3200 isconstructed from a transparent material, e.g. a transparentpolycarbonate. The use of a transparent material can reduce theobtrusiveness of the patient interface, and help improve compliance withtherapy. The use of a transparent material can aid a clinician toobserve how the patient interface is located and functioning.

In certain forms of the present technology, the plenum chamber 3200 isconstructed from a translucent material. The use of a translucentmaterial can reduce the obtrusiveness of the patient interface, and helpimprove compliance with therapy.

4.3.3 Positioning and Stabilising Structure

The seal-forming structure 3100 of the patient interface 3000 of thepresent technology may be held in sealing position in use by thepositioning and stabilising structure 3300.

In one form the positioning and stabilising structure 3300 provides aretention force at least sufficient to overcome the effect of thepositive pressure in the plenum chamber 3200 to lift off the face.

In one form the positioning and stabilising structure 3300 provides aretention force to overcome the effect of the gravitational force on thepatient interface 3000.

In one form the positioning and stabilising structure 3300 provides aretention force as a safety margin to overcome the potential effect ofdisrupting forces on the patient interface 3000, such as from tube drag,or accidental interference with the patient interface.

In one form of the present technology, a positioning and stabilisingstructure 3300 is provided that is configured in a manner consistentwith being worn by a patient while sleeping. In one example thepositioning and stabilising structure 3300 has a low profile, orcross-sectional thickness, to reduce the perceived or actual bulk of theapparatus. In one example, the positioning and stabilising structure3300 comprises at least one strap having a rectangular cross-section. Inone example the positioning and stabilising structure 3300 comprises atleast one flat strap.

In one form of the present technology, a positioning and stabilisingstructure 3300 is provided that is configured so as not to be too largeand bulky to prevent the patient from lying in a supine sleepingposition with a back region of the patient's head on a pillow.

In one form of the present technology, a positioning and stabilisingstructure 3300 is provided that is configured so as not to be too largeand bulky to prevent the patient from lying in a side sleeping positionwith a side region of the patient's head on a pillow.

In one form of the present technology, a positioning and stabilisingstructure 3300 is provided with a decoupling portion located between ananterior portion of the positioning and stabilising structure 3300, anda posterior portion of the positioning and stabilising structure 3300.The decoupling portion does not resist compression and may be, e.g. aflexible or floppy strap. The decoupling portion is constructed andarranged so that when the patient lies with their head on a pillow, thepresence of the decoupling portion prevents a force on the posteriorportion from being transmitted along the positioning and stabilisingstructure 3300 and disrupting the seal.

In one form of the present technology, a positioning and stabilisingstructure 3300 comprises a strap constructed from a laminate of a fabricpatient-contacting layer, a foam inner layer and a fabric outer layer.In one form, the foam is porous to allow moisture, (e.g., sweat), topass through the strap. In one form, the fabric outer layer comprisesloop material to engage with a hook material portion.

In certain forms of the present technology, a positioning andstabilising structure 3300 comprises a strap that is extensible, e.g.resiliently extensible. For example the strap may be configured in useto be in tension, and to direct a force to draw a seal-forming structureinto sealing contact with a portion of a patient's face. In an examplethe strap may be configured as a tie.

In one form of the present technology, the positioning and stabilisingstructure comprises a first tie, the first tie being constructed andarranged so that in use at least a portion of an inferior edge thereofpasses superior to an otobasion superior of the patient's head andoverlays a portion of the parietal bone without overlaying the occipitalbone.

In one form of the present technology suitable for a nasal-only mask orfor a full-face mask, the positioning and stabilising structure includesa second tie, the second tie being constructed and arranged so that inuse at least a portion of a superior edge thereof passes inferior to anotobasion inferior of the patient's head and overlays or lies inferiorto the occipital bone of the patient's head.

In one form of the present technology suitable for a nasal-only mask orfor a full-face mask, the positioning and stabilising structure includesa third tie that is constructed and arranged to interconnect the firsttie and the second tie to reduce a tendency of the first tie and thesecond tie to move apart from one another.

In certain forms of the present technology, a positioning andstabilising structure 3300 comprises a strap that is bendable and e.g.non-rigid. An advantage of this aspect is that the strap is morecomfortable for a patient to lie upon while the patient is sleeping.

In certain forms of the present technology, a positioning andstabilising structure 3300 comprises a strap constructed to bebreathable to allow moisture vapour to be transmitted through the strap,

In certain forms of the present technology, a system is providedcomprising more than one positioning and stabilizing structure 3300,each being configured to provide a retaining force to correspond to adifferent size and/or shape range. For example the system may compriseone form of positioning and stabilizing structure 3300 suitable for alarge sized head, but not a small sized head, and another. suitable fora small sized head, but not a large sized head.

4.3.4 Vent

In one form, the patient interface 3000 includes a vent 3400 constructedand arranged to allow for the washout of exhaled gases, e.g. carbondioxide.

In certain forms the vent 3400 is configured to allow a continuous ventflow from an interior of the plenum chamber 3200 to ambient whilst thepressure within the plenum chamber is positive with respect to ambient.The vent 3400 is configured such that the vent flow rate has a magnitudesufficient to reduce rebreathing of exhaled CO₂ by the patient whilemaintaining the therapeutic pressure in the plenum chamber in use.

The vent 3400 may take various forms. In one form, vent 3400, inaccordance with the present technology, comprises a plurality of holes,for example, about 20 to about 80 holes, or about 40 to about 60 holes,or about 45 to about 55 holes. The size of each hole may be between 0.5and 1 mm, preferably between 0.6 and 0.9 mm and more preferably between0.7 and 0.8 mm. Whilst the holes are usually formed with circularopenings, other shapes are also possible. A number of smaller holes maybe replaced by one or more larger holes. Some of the larger holes mayhave the form of slits.

The vent 3400 may be located on and integrated within the plenum chamber3200 or within the elbow 3600. Alternatively, the vent 3400 may beformed separately as a decoupling structure, e.g., a swivel, that can belocated as part of the air circuit 4170 or between the air circuit 4170and the plenum chamber 3200.

FIG. 4A illustrates an implementation of a vent 3400 (e.g., a gaswashout vent). FIG. 4A is a cross-section through passages 3402, a wall3404, a diffusing material 3406, and a housing 3408, each of which arearound a central air passage 3410. The air passage 3410 may be part ofan inlet to the plenum chamber 3200 (e.g., part of a decouplingstructure) or may be part of the air circuit 4170. The illustratedcross-section includes some amount of symmetry about the central airpassage 3410, but symmetry is not required.

The diffusing material 3406 is spaced away from the wall 3404 by a gap3412 and thus provides a passage with uninterrupted fluid communicationbetween the passages 3402 and an opening 3416. This is provided bylocating the diffusing material at least partially in the housing sothat a surface 3414 of the diffusing material 3406 faces the surface ofopenings 3420. The surface 3414 of the diffusing material is asubstantially planar surface and is spaced away from the surface ofopenings 3420 by the gap 3412. The configuration is such that the gapextends to provide fluid communication between all of the openings 3420,as well as between all of the openings 3420 and the opening 3416.

The opening 3416 provides communication with ambient atmosphere. Thesize of the gap should be such that it would allow any dust accumulatedin the gap to be cleaned and any accumulated water to be dried out. Thusthe gap 3412 can be between 1 and 3 mm deep, preferably between 1.5 and2.5 mm and even more preferably, about 2 mm. As it would be discussedlater in the text, the arrangement is such that during the standardoperation of the patient interface, at least some pressurised airexiting the passages 3402 (for example, a jet or pressure wave) bridgesthe gap 3412 and enters the diffusing material 3406. Once the airflowenters the diffusing material, the nature of the material forces theairflow onto a tortuous path. The air may enter the diffusing material3406, even though a path of lower resistance exists via the gap 3412, ifa jet of air, which may be at or approaching sonic velocity, impartssufficient momentum on the air that at least some molecules enter thediffusing material.

The properties of the diffusing material 3406, such as thickness ordensity, as well as the size of openings 3424, are chosen so that theopenings 3424 have a negligible effect on the overall airflow. Also, asecond wall 3428 is directly opposite the passages 3402 with respect tothe diffusing material 3406. Thus the housing 3408 is essentially closedfor the airflow on that opposite side. Because of that, the airflow thatenters the diffusing material 3406 is forced to eventually return backinto the gap 3412 and out to the ambient air via the opening 3416. Thetortuous path forced on the airflow by the above described configurationof the vent substantially reduces the jetting effect and/or noisegenerated by the jetting effect associated with the vent. Alternativelyor additionally, because the diffusing material 3406 defines at leastone side of the gap 3412, any sound waves propagating through the gapwill be able to expand into the diffusing material 3406 and reduce thesound level, even if there is little or no net flow of air through thediffusing material 3406 itself.

As illustrated, the gap 3412 extends all along a surface 3414 of thediffusing material 3406 to the opening 3416, but the gap 3412 need notextend along this entire length. For example, there could be no gap at aportion 3418 (e.g., interior to a passage 3402 closest to the airpassage 3410, which is radially inward in the illustratedimplementation). Other configurations of the gap 3412 that provide anuninterrupted path from the passages 3402 to the opening 3416 may alsobe provided.

With the gap 3412, the performance characteristics of the vent 3400 maybe improved compared to a vent without the gap. For example, somematerials suitable for the diffusing material 3406 may be difficult tomanufacture with consistent density and air permeability. This may causean unwanted variation in the washout airflow through the vents ofdifferent patient interfaces. The introduction of the gap offers apermanent escape path and results in a more consistent and/orpredictable washout flow. The gap offers a further advantage when theairflow through the diffusing material 3406 is reduced or prevented forany reason, such as if the material 3406 has become wet. In this casethe gap 3412 offers an escape path for the air to the ambientatmosphere.

The wall 3404 separates the diffusing material 3406 from an interiorportion of the patient interface 3000 that is exposed to therapypressure during use. The passages 3402 are illustrated as being throughthe wall 3404 and include respective openings 3420 adjacent to andfacing toward the diffusing material 3406. The passages 3402 may be anynumber and of any geometric configuration that provides the desired flowcharacteristics of the vent 3400. For example, the passages could becylindrical passages, frusto-conical passages and/or any otherthree-dimensional shape (such as a slot) that provides desiredperformance characteristics of the vent 3400. Whilst in FIG. 4A thepassages are of a frusto-conical shape with a tapered down openingoriented towards the diffused material, this does not have to be thecase and the tapered down opening of the frusto-conical shape may beoriented in the opposite direction. Any or all of these configurationsmay provide fluid communication with an interior portion of the patientinterface 3000 that is configured to be exposed to the therapy pressure.A single passage 3402 may be provided, or a plurality may be provided,but providing a plurality may reduce any audible sound generated. Thepassages 3402 may be passive or part of a valve system (not shown) thatregulates flow through the passage based on conditions such as therapypressure. The openings 3420 and/or the passages 3402 are sized, and theopenings 3420 and the diffusing material 3406 are oriented, so that airexiting the openings 3420 may impinge on the diffusing material 3406 atthe surface 3414 when an interior portion of the patient interface 3000is exposed to the therapy pressure. Air exiting the openings 3420 mayalso impinge when the interior portion is exposed to pressures lowerthan the therapy pressure. With this configuration, at least a portionof air exiting an opening 3420 may penetrate into the diffusing material3406 when the interior portion of the patient interface 3000 is exposedto the therapy pressure, and then exit from the surface 3414 beforeexiting the vent via the opening 3416. Any portion of air thatpenetrates the diffusing material 3406 but that does not exit thesurface 3414 may exit the diffusing material 3406 elsewhere due to leaksin the housing 3408. This flow configuration may result in the overallflow path for gas exiting the vent 3400 being more tortious, andtherefore more likely to dampen or eliminate noise generated. Air mayimpinge but not penetrate if the velocity is sufficiently low and theporosity of the surface 3414 is such that surface effects prevent theair from penetrating. In this scenario, the diffusing material 3406 maystill provide reduction in the jetting effect, as well as a noisereduction by allowing sound waves to propagate into the diffusingmaterial 3406 and dissipate.

The diffusing material 3406 may cause diffusion of air as the air passesthrough the material, which may absorb the energy and/or reduce the airvelocity. Reducing the velocity of flow reduces the associated noise,which is often due to turbulence of flow or air jets colliding with hardsurfaces. The diffusing material 3406 may be fibrous material similar tothat used in filter media (e.g., uncompressed fibres, such as polyesterfibres) or open-celled foam. Any material that allows at least partialpenetration by the air flow and that provides a tortious path for airflowing through the material may be used for the diffusing material3406. The diffusing material can be a moisture wicking material such assintered plastic. The diffusing material may also be hydrophobic and maybe processed to have antibacterial properties. One or more of theseconfigurations may aid with removal of moisture, which may be beneficialduring cleaning.

The housing 3408 may have any shape that facilitates the retention ofthe diffusing material 3406 in place while also providing the desiredflow characteristics of the vent 3400. The housing 3408 is illustratedto include a wall configuration that prevents air from flowing out ofthe housing at all areas directly opposite each of the openings 3420.The housing 3408 may include all of the structural components thatsurround the diffusing material 3406 such as the wall 3404 and the wall3428. A center line 3430 is illustrated along a central axis of each ofthe passages 3402 and extends to the second wall 3428. If the passagesare sufficiently long relative to inlet flow conditions, a fullydeveloped flow will occur and the arrows 3422 will be approximations offlow vectors through and exiting from the passages 3402. The chaoticnature of fluid flow may result in the actual flow diverging anddissipating as the flow moves away from the passages 3402. However avector, e.g., a magnitude and direction, may be used to characterize theflow at a given point. If these vectors are extended they willeventually intersect a portion of the housing 3408 that is devoid ofopenings. However, it is not only the flow vectors that generally extendalong the central axes of the respective openings, which if extended inthe direction of the flow will encounter a solid wall. If thecross-sectional area of each of the openings 3420 is projected along therespective center line 3430, the image of the area will be projectedover a solid portion of the wall 3428 instead of an opening in the wall3428. Thus no opening (e.g., the second opening 3424) in the housing3408, or vent 3400, is in-line with an exit vector or overlaps with aprojected area from any of the passages 3402 and air exiting thepassages 3402 cannot exit the vent 3400 from a portion of the secondwall 3428 that is directly opposite the passages 3402. Instead, the exitopening 3416 extends in a direction that is at an angle with respect tothe passage 3402 flow vectors. The angle could be acute, but in someexamples it is straight (e.g., a right angle to the exit vectors) oreven obtuse. Such a configuration increases the likelihood that airexiting the passages 3402 will follow a tortious path through thediffusing material 3406 to exit the vent 3400 through openings 3416. Aswas mentioned before, the exit opening 3416 may be defined by one ormore of the following: walls of the housing 3408, a surface of thediffusing material or a surface of another component. The exit opening3416 could be oriented in any direction, as long as it releases the airinto the ambient environment along a path that does not pass through thediffusing material 3406. In one alternative example, the flow out of theexit opening 3416 can be parallel to, but offset from, the arrows 3422.

As illustrated, the housing 3408 partly bounds the opening 3416 and thewall 3404 also partly bounds the opening 3416, but the opening 3416 canbe bounded completely by the housing 3408 or not bounded at all by thehousing 3408. In the latter case, the opening 3416 can, for example, bedefined by a component other than the housing 3408. Any configurationand location of the opening 3416 that provides the appropriate flowpath, including the gap 3412, may be utilized. As illustrated, theopening 3416 is an annular gap all around the periphery of the vent3400, but the opening 3416 may be any number of openings. For example,it may be desirable to divide the opening 3416 into a plurality ofopenings to increase the stability of the resultant openings. Asillustrated, the opening 3416 may be described as a direct exit toambient, but the opening 3416 could be a less direct, or more tortious,path to ambient. For example, there could be additional structuralelements that result in the flow path including one or more turns beforeexiting to ambient. Also, the opening 3416 could be at a differentorientation with respect to the gap 3412 or wall 3404 than illustrated.As illustrated the flow path through the opening 3416 is substantially aright angle to the passages 3402 and/or arrows 3422, but the opening maybe at other angles or orientations. For example, the flow path throughthe opening could be at an obtuse or acute angle to the passages 3402 orcould be parallel to and offset from the passages 3402.

The housing 3408 may also include openings 3424 that are not in-linewith the passages 3402. The openings 3424 are illustrated with a centerline 3432 on the central axis of the openings 3424 to visually clarifythe orientation of the openings 3424. The center lines 3430 of thepassages 3402 are not aligned with the center lines 3432 of the openings3424. The openings 3424 may be optionally included (zero, one or moremay be included) to allow for water removal after cleaning the vent3400. The openings 3424 may allow water to be shaken out of the vent3400 and/or allow greater opportunity for water to evaporate and exitthe vent 3400, where both shaking and evaporation contribute to dryingthe vent 3400. If the openings 3424 are included, they are preferablylocated and sized so that, in conjunction with the diffusing material3406, opening 3416 and gap 3412, substantially no air exits the openings3424 when therapy pressure is applied to the patient interface 3000. Inorder to determine flow out of the openings 3424, pressure may beapplied to the patient interface 3000 and the flow rate through the vent3400 is measured. Then, the openings 3424 may be completely blocked andthe flow rate re-measured. If the flow rate decreases by less than apredetermined percentage, then there is substantially no decrease in airflow through the vent 3400. Preferably, the flow rate decreases by nomore than 5%, and more preferably the flow rate decreases by no morethan 3%. In fact, blocking the openings 3424 may cause no change in theflow rate through the vent 3400. By designing the vent 3400 so thatcompletely blocking the openings 3424 results in substantially no changein flow through the vent 3400, the vent 3400 should provide sufficientgas-washout even if the diffusing material 3406 becomes completelyclogged, which could occur due to water or mucous build-up.

The openings 3424 may be formed in an area adjacent the side of thediffusing material 3406 that is opposite to the side facing the openings3420. However, the size and the location of the openings 3424 can vary.The openings 3424 may have at least two purposes—to allow the vent to bewashed and dried. First, the openings 3424 may allow the diffusingmaterial 3406 to be washed by a user by way of placing the entire vent3400 under water from a faucet. For washing to be effective, theopenings 3424 are preferably sufficiently large to allow liquid water(e.g., droplets) to enter the housing. Second, the openings 3424 mayallow, after a wash or after an inadvertent accumulation of liquid(e.g., mucous, water, etc.) during use of the vent, for the removal ofthe accumulated liquid. The size of each single opening 3424 is relatedto the ability to allow liquid such as water to move in and out of theevent. The combined size of all of the openings may determine howefficiently the vent is washed and dried. A combined area of between 20mm² and 80 mm² is believed to be able to allow adequate washing anddrying. In some examples, the total opening areas is preferably between30 and 60 mm², and even more preferably around 50 mm². The location ofthe openings may also be significant. It is preferable that openings3424 are spaced from and located, at least to an extent, opposite to theopenings 3416 with respect to the diffusing material 3406. This providesa water or liquid flow path between openings 3416 and 3424, whichimproves the ability to clean and dry the diffusing material 3406. Withat least the embodiment illustrated in FIG. 4A, water may be removed atleast through the second opening 3424 by shaking, or applyingcentripetal force to, the vent 3400.

The housing 3408 may hold the diffusing material 3406 is place by anysuitable method. For example, the housing 3408 and diffusing material3406 may be bonded together (e.g., glued or melted together) ormechanically fastened (e.g., friction, interference, detent, etc.).

The housing 3408 may be a single integral piece or multiple pieces ormultiple pieces joined together into a single piece. The wall 3404 maybe permanently joined to, or integrally formed with, the housing 3408.The housing may be attached to the vent 3400 in a non-releasable manner,which is attachment that is not intended to be detached withoutbreaking. Non-releasable attachment may include glue, ultrasonicwelding, melting with a hot iron, one-time snap fit (e.g., snap fit thatis designed to break upon separation), originally formed as one piece,etc. If the housing 3408 is formed such that the housing 3408 and/or thediffusing material 3406 cannot be removed, some benefits may beachieved. For example, if the housing 3408 and/or the diffusing material3406 cannot be removed, incorrect user installation or inadvertentdetachment of the vent can be avoided.

FIG. 4B illustrates another configuration of the vent 3400. Thedescriptions associated with the reference numbers of FIG. 4A are alsoapplicable here, and thus not repeated. This configuration of the vent3400 is similar to that illustrated in FIG. 4A except that the airpassage 3410 is omitted. Thus the gap 3412 extends from one side of thevent 3400 to the other.

FIG. 4C illustrates another configuration of the vent 3400. Thedescriptions associated with the reference numbers of FIG. 4A are alsoapplicable here, and thus not repeated. Here, the air passage 3410 isomitted and instead a member 3426 is illustrated, which may secure thediffusing material 3406 and/or housing 3408.

FIG. 4D illustrates another configuration of the vent 3400. Thedescriptions associated with the reference numbers of FIG. 4A are alsoapplicable here, and thus not repeated. This figure differs from FIG. 4Ain that the locations of the openings 3424 are different. This figurealso illustrates that the opening 3416 may be a continuous opening allaround a periphery of the vent 3400. The openings 3424 may also becontinuous, however are preferably discontinuous from each other and/orfrom the opening 3416.

FIG. 4E illustrates another configuration of the vent 3400. Thedescriptions associated with the reference numbers of FIG. 4A are alsoapplicable here, and thus not repeated. In this configuration, thepassages 3402 are in communication with and arrayed around the airpassage 3410, resulting in the vent 3400 having an overall annularconfiguration compared to the planar configuration of FIGS. 4A-4D. Inother words, the passages 3402 in FIGS. 4A-4D are in one planar ornear-planar wall 3404, whereas the wall 3404 in FIG. 4E is cylindricaland the gas exiting the vent 3400 exits along the cylinder axisindicated with an interrupted line.

FIG. 4F illustrates another configuration of the vent 3400. Thedescriptions associated with the reference numbers of FIG. 4A are alsoapplicable here, and thus not repeated. FIG. 4F is similar to FIG. 4Eexcept that opening 3416 is provided at two ends of the diffusingmaterial 3406 in FIG. 4F, but only at one end in FIG. 4E.

In each of FIGS. 4A-4F, the arrows illustrated through the diffusingmaterial 3406 are conceptual illustrations of air flow through thediffusing material 3406 and may not be representative of actual air flowthrough the diffusing material 3406. In general, each of these arrowsshows the concept of air exiting the passages 3402, entering thediffusing material 3406 via the surface 3414, exiting the diffusingmaterial via the surface 3414, flowing through the gap 3412 and then toambient via the opening 3416.

FIGS. 4G-4I illustrate another configuration of the vent 3400. Thedescriptions associated with the reference numbers of FIG. 4A are alsoapplicable here, and thus not repeated except as noted. FIG. 4Gillustrates an example of the vent 3400 in a perspective view, where thevent 3400 is an insertable and/or removable assembly. FIG. 4H is a topview where a top cover 3440 has been omitted so that the interiorstructure is visible. FIG. 4I is a cross-sectional view of FIG. 4H, butwith the top cover included. This configuration of the vent 3400 issimilar to that illustrated in FIG. 4B in that the air passage 3410 isomitted (but could be included if desired). As best seen in FIG. 4I, asupport 3434 contacts the surface 3414 to support the diffusing material3406. As illustrated in FIGS. 4H and 4I, the support 3434 is illustratedas a contiguous wall that bisects the gap 3412, extending uninterruptedfrom one side to another. However, the support 3434 need not becontiguous and could be a formed by one or more non-contiguous supports(one or more gaps could be provided in the support 3434).

Another difference is the position of the openings 3416. Instead ofbeing substantially in line with the gap 3412, the openings 3416 areoffset in a direction away from the surface that includes openings 3420,resulting in a second portion 3412A of the gap 3412 around a peripheryof the diffusing material 3406. With this arrangement, the air can flowinto the surface 3414 and out of a lateral surface 3436 of the diffusingmaterial 3406 before flowing out through the openings 3416. The air canalso flow through the gap 3412 and the second portion 3412A withoutpassing through the diffusing material 3406. With the chaotic andunpredictable nature of the flow of individual molecules, the actual airflow may be a combination of both flow paths. However, by providing bothflow paths, the vent 3400 may provide adequate flow even if thediffusing material 3406 becomes clogged.

FIGS. 4G and 4I illustrate a groove 3438 around a perimeter of the vent3400. Such a groove may allow for the vent 3400 to be retained in amating hole, preferably in a replaceable manner. If, for example, thehole is made in a relatively flexible material such as silicone, thevent 3400 may be readily removed so that actions such as cleaning orreplacement can be performed in a simple manner.

FIGS. 4J and 4K illustrate aspects similar to FIG. 4I but with theaddition of a deflector 3442. In FIG. 4J, the deflector 3442 isillustrated as a solid, flat obstruction that prevents air flowingstraight through the diffusing material 3406 to the wall 3428 (e.g., outan opposite side from the surface 3414). In FIG. 4K, the deflector 3442is curved in a manner that may generate a more smooth transition out ofthe sides of the diffusing material 3406 than the flat deflectorillustrated in FIG. 4J. Although multiple pieces of the deflector 3442are illustrated in FIG. 4K, any number of pieces, including a singlepiece, may be utilized as necessary for achieving desired flowcharacteristics. For both versions of the deflector 3442, any suitablemethod for producing the deflector 3442 within the diffusing material3406 may be used. For example, an appropriately shaped cut in the sideof the diffusing material 3406 may allow for insertion of the deflector3442. Alternatively, the diffusing material 3406 may be made frommultiple pieces that are then joined around the diffusing material 3406.

In one aspect, the diffusing material 3406 may be removable. Forexample, if the cover 3440 is attached in a releasable manner, thediffusing material 3406 may be retained through mechanical retention byway of the cover 3440. If the cover 3440 is removed, the diffusingmaterial 3406 could also be removed. However, the diffusing material3406 may not be removable in another aspect. For example, if the cover3440 is attached to the vent 3400 such that the cover can only beremoved by damage to the vent 3400, the diffusing material 3406 may beconsidered not removable. Alternatively, the diffusing material 3406could be attached within the vent 3400 in a permanent manner, such as byadhesive, so that the diffusing material 3406 would be damaged duringremoval. Even if the cover 3440 is removable without causing damage, thediffusing material 3406 could be fixed in a manner that would damage ordestroy the diffusing material 3406, thus making the diffusing material3406 not removable.

Although a boundary of the diffusing material 3406 is described as asurface 3414, it may be different from a surface as of a solid body. Thediffusing material 3406 may have many openings or gaps to allow tortiousflow through the diffusing material. Thus the surface 3414 may also beconsidered a boundary of the diffusing material 3406.

The vent 3400 may produce relatively low volume of noise or suppressnoise generated before the sound waves propagate to a user. Preferably,the sound generated is less than 28 dB(A). For example, the sound may be20-28 dB(A), 22-26 dB(A), or about 24 dB(A). These sound levels may besufficiently low that neither the user nor a bed partner is disturbed.

4.3.5 Decoupling Structure(s)

In one form the patient interface 3000 includes at least one decouplingstructure, for example, a swivel or a ball and socket.

4.3.6 Connection Port

Connection port 3600 allows for connection to the air circuit 4170.

4.3.7 Forehead Support

In one form, the patient interface 3000 includes a forehead support3700.

4.3.8 Anti-Asphyxia Valve

In one form, the patient interface 3000 includes an anti-asphyxia valve.

4.3.9 Ports

In one form of the present technology, a patient interface 3000 includesone or more ports that allow access to the volume within the plenumchamber 3200. In one form this allows a clinician to supply supplementaloxygen. In one form, this allows for the direct measurement of aproperty of gases within the plenum chamber 3200, such as the pressure.

4.4 Glossary

For the purposes of the present technology disclosure, in certain formsof the present technology, one or more of the following definitions mayapply. In other forms of the present technology, alternative definitionsmay apply.

4.4.1 General

Air: In certain forms of the present technology, air may be taken tomean atmospheric air, and in other forms of the present technology airmay be taken to mean some other combination of breathable gases, e.g.atmospheric air enriched with oxygen.

Ambient: In certain forms of the present technology, the term ambientwill be taken to mean (i) external of the treatment system or patient,and (ii) immediately surrounding the treatment system or patient.

For example, ambient humidity with respect to a humidifier may be thehumidity of air immediately surrounding the humidifier, e.g. thehumidity in the room where a patient is sleeping. Such ambient humiditymay be different to the humidity outside the room where a patient issleeping.

In another example, ambient pressure may be the pressure immediatelysurrounding or external to the body.

In certain forms, ambient (e.g., acoustic) noise may be considered to bethe background noise level in the room where a patient is located, otherthan for example, noise generated by an RPT device or emanating from amask or patient interface. Ambient noise may be generated by sourcesoutside the room.

Automatic Positive Airway Pressure (APAP) therapy: CPAP therapy in whichthe treatment pressure is automatically adjustable, e.g. from breath tobreath, between minimum and maximum limits, depending on the presence orabsence of indications of SDB events.

Continuous Positive Airway Pressure (CPAP) therapy: Respiratory pressuretherapy in which the treatment pressure is approximately constantthrough a respiratory cycle of a patient. In some forms, the pressure atthe entrance to the airways will be slightly higher during exhalation,and slightly lower during inhalation. In some forms, the pressure willvary between different respiratory cycles of the patient, for example,being increased in response to detection of indications of partial upperairway obstruction, and decreased in the absence of indications ofpartial upper airway obstruction.

Flow rate: The volume (or mass) of air delivered per unit time. Flowrate may refer to an instantaneous quantity. In some cases, a referenceto flow rate will be a reference to a scalar quantity, namely a quantityhaving magnitude only. In other cases, a reference to flow rate will bea reference to a vector quantity, namely a quantity having bothmagnitude and direction. Flow rate may be given the symbol Q. ‘Flowrate’ is sometimes shortened to simply ‘flow’ or ‘airflow’.

In the example of patient respiration, a flow rate may be nominallypositive for the inspiratory portion of a breathing cycle of a patient,and hence negative for the expiratory portion of the breathing cycle ofa patient. Total flow rate, Qt, is the flow rate of air leaving the RPTdevice. Vent flow rate, Qv, is the flow rate of air leaving a vent toallow washout of exhaled gases. Leak flow rate, Ql, is the flow rate ofleak from a patient interface system or elsewhere. Respiratory flowrate, Qr, is the flow rate of air that is received into the patient'srespiratory system.

Humidifier: The word humidifier will be taken to mean a humidifyingapparatus constructed and arranged, or configured with a physicalstructure to be capable of providing a therapeutically beneficial amountof water (H₂O) vapour to a flow of air to ameliorate a medicalrespiratory condition of a patient.

Leak: The word leak will be taken to be an unintended flow of air. Inone example, leak may occur as the result of an incomplete seal betweena mask and a patient's face. In another example leak may occur in aswivel elbow to the ambient.

Noise, conducted (acoustic): Conducted noise in the present documentrefers to noise which is carried to the patient by the pneumatic path,such as the air circuit and the patient interface as well as the airtherein. In one form, conducted noise may be quantified by measuringsound pressure levels at the end of an air circuit.

Noise, radiated (acoustic): Radiated noise in the present documentrefers to noise which is carried to the patient by the ambient air. Inone form, radiated noise may be quantified by measuring soundpower/pressure levels of the object in question according to ISO 3744.

Noise, vent (acoustic): Vent noise in the present document refers tonoise which is generated by the flow of air through any vents such asvent holes of the patient interface.

Patient: A person, whether or not they are suffering from a respiratorycondition.

Pressure: Force per unit area. Pressure may be expressed in a range ofunits, including cmH₂O, g-f/cm² and hectopascal. 1 cmH₂O is equal to 1g-f/cm² and is approximately 0.98 hectopascal. In this specification,unless otherwise stated, pressure is given in units of cmH₂O.

The pressure in the patient interface is given the symbol Pm, while thetreatment pressure, which represents a target value to be achieved bythe mask pressure Pm at the current instant of time, is given the symbolPt.

Respiratory Pressure Therapy (RPT): The application of a supply of airto an entrance to the airways at a treatment pressure that is typicallypositive with respect to atmosphere.

Ventilator: A mechanical device that provides pressure support to apatient to perform some or all of the work of breathing.

4.4.1.1 Materials

Silicone or Silicone Elastomer: A synthetic rubber. In thisspecification, a reference to silicone is a reference to liquid siliconerubber (LSR) or a compression moulded silicone rubber (CMSR). One formof commercially available LSR is SILASTIC (included in the range ofproducts sold under this trademark), manufactured by Dow Corning.Another manufacturer of LSR is Wacker. Unless otherwise specified to thecontrary, an exemplary form of LSR has a Shore A (or Type A) indentationhardness in the range of about 35 to about 45 as measured using ASTMD2240.

Polycarbonate: a thermoplastic polymer of Bisphenol-A Carbonate.

4.4.1.2 Mechanical Properties

Resilience: Ability of a material to absorb energy when deformedelastically and to release the energy upon unloading.

Resilient: Will release substantially all of the energy when unloaded.Includes e.g. certain silicones, and thermoplastic elastomers.

Hardness: The ability of a material per se to resist deformation (e.g.described by a Young's Modulus, or an indentation hardness scalemeasured on a standardised sample size).

-   -   ‘Soft’ materials may include silicone or thermo-plastic        elastomer (TPE), and may, e.g. readily deform under finger        pressure.    -   ‘Hard’ materials may include polycarbonate, polypropylene, steel        or aluminium, and may not e.g. readily deform under finger        pressure.

Stiffness (or rigidity) of a structure or component: The ability of thestructure or component to resist deformation in response to an appliedload. The load may be a force or a moment, e.g. compression, tension,bending or torsion. The structure or component may offer differentresistances in different directions.

Floppy structure or component: A structure or component that will changeshape, e.g. bend, when caused to support its own weight, within arelatively short period of time such as 1 second.

Rigid structure or component: A structure or component that will notsubstantially change shape when subject to the loads typicallyencountered in use. An example of such a use may be setting up andmaintaining a patient interface in sealing relationship with an entranceto a patient's airways, e.g. at a load of approximately 20 to 30 cmH₂Opressure.

As an example, an I-beam may comprise a different bending stiffness(resistance to a bending load) in a first direction in comparison to asecond, orthogonal direction. In another example, a structure orcomponent may be floppy in a first direction and rigid in a seconddirection.

4.4.2 Respiratory Cycle

Apnea: According to some definitions, an apnea is said to have occurredwhen flow falls below a predetermined threshold for a duration, e.g. 10seconds. An obstructive apnea will be said to have occurred when,despite patient effort, some obstruction of the airway does not allowair to flow. A central apnea will be said to have occurred when an apneais detected that is due to a reduction in breathing effort, or theabsence of breathing effort, despite the airway being patent. A mixedapnea occurs when a reduction or absence of breathing effort coincideswith an obstructed airway.

Breathing rate: The rate of spontaneous respiration of a patient,usually measured in breaths per minute.

Duty cycle: The ratio of inhalation time, Ti to total breath time, Ttot.

Effort (breathing): The work done by a spontaneously breathing personattempting to breathe.

Expiratory portion of a breathing cycle: The period from the start ofexpiratory flow to the start of inspiratory flow.

Flow limitation: Flow limitation will be taken to be the state ofaffairs in a patient's respiration where an increase in effort by thepatient does not give rise to a corresponding increase in flow. Whereflow limitation occurs during an inspiratory portion of the breathingcycle it may be described as inspiratory flow limitation. Where flowlimitation occurs during an expiratory portion of the breathing cycle itmay be described as expiratory flow limitation.

Types of flow limited inspiratory waveforms:

(i) Flattened: Having a rise followed by a relatively flat portion,followed by a fall.

(ii) M-shaped: Having two local peaks, one at the leading edge, and oneat the trailing edge, and a relatively flat portion between the twopeaks.

(iii) Chair-shaped: Having a single local peak, the peak being at theleading edge, followed by a relatively flat portion.

(iv) Reverse-chair shaped: Having a relatively flat portion followed bysingle local peak, the peak being at the trailing edge.

Hypopnea: According to some definitions, a hypopnea is taken to be areduction in flow, but not a cessation of flow. In one form, a hypopneamay be said to have occurred when there is a reduction in flow below athreshold rate for a duration. A central hypopnea will be said to haveoccurred when a hypopnea is detected that is due to a reduction inbreathing effort. In one form in adults, either of the following may beregarded as being hypopneas:

-   -   (i) a 30% reduction in patient breathing for at least 10 seconds        plus an associated 4% desaturation; or    -   (ii) a reduction in patient breathing (but less than 50%) for at        least 10 seconds, with an associated desaturation of at least 3%        or an arousal.

Hyperpnea: An increase in flow to a level higher than normal.

Inspiratory portion of a breathing cycle: The period from the start ofinspiratory flow to the start of expiratory flow will be taken to be theinspiratory portion of a breathing cycle.

Patency (airway): The degree of the airway being open, or the extent towhich the airway is open. A patent airway is open. Airway patency may bequantified, for example with a value of one (1) being patent, and avalue of zero (0), being closed (obstructed).

Positive End-Expiratory Pressure (PEEP): The pressure above atmospherein the lungs that exists at the end of expiration.

Peak flow rate (Qpeak): The maximum value of flow rate during theinspiratory portion of the respiratory flow waveform.

Respiratory flow rate, patient airflow rate, respiratory airflow rate(Qr): These terms may be understood to refer to the RPT device'sestimate of respiratory flow rate, as opposed to “true respiratory flowrate” or “true respiratory flow rate”, which is the actual respiratoryflow rate experienced by the patient, usually expressed in litres perminute.

Tidal volume (Vt): The volume of air inhaled or exhaled during normalbreathing, when extra effort is not applied.

(inhalation) Time (Ti): The duration of the inspiratory portion of therespiratory flow rate waveform.

(exhalation) Time (Te): The duration of the expiratory portion of therespiratory flow rate waveform.

(total) Time (Ttot): The total duration between the start of oneinspiratory portion of a respiratory flow rate waveform and the start ofthe following inspiratory portion of the respiratory flow rate waveform.

Typical recent ventilation: The value of ventilation around which recentvalues of ventilation Vent over some predetermined timescale tend tocluster, that is, a measure of the central tendency of the recent valuesof ventilation.

Upper airway obstruction (UAO): includes both partial and total upperairway obstruction. This may be associated with a state of flowlimitation, in which the flow rate increases only slightly or may evendecrease as the pressure difference across the upper airway increases(Starling resistor behaviour).

Ventilation (Vent): A measure of a rate of gas being exchanged by thepatient's respiratory system. Measures of ventilation may include one orboth of inspiratory and expiratory flow, per unit time. When expressedas a volume per minute, this quantity is often referred to as “minuteventilation”. Minute ventilation is sometimes given simply as a volume,understood to be the volume per minute.

4.4.3 Ventilation

Adaptive Servo-Ventilator (ASV): A servo-ventilator that has achangeable, rather than fixed target ventilation. The changeable targetventilation may be learned from some characteristic of the patient, forexample, a respiratory characteristic of the patient.

Backup rate: A parameter of a ventilator that establishes the minimumbreathing rate (typically in number of breaths per minute) that theventilator will deliver to the patient, if not triggered by spontaneousrespiratory effort.

Cycled: The termination of a ventilator's inspiratory phase. When aventilator delivers a breath to a spontaneously breathing patient, atthe end of the inspiratory portion of the breathing cycle, theventilator is said to be cycled to stop delivering the breath.

Expiratory positive airway pressure (EPAP): a base pressure, to which apressure varying within the breath is added to produce the desired maskpressure which the ventilator will attempt to achieve at a given time.

End expiratory pressure (EEP): Desired mask pressure which theventilator will attempt to achieve at the end of the expiratory portionof the breath. If the pressure waveform template Π(Φ) is zero-valued atthe end of expiration, i.e. Π(Φ)=0 when Φ=1, the EEP is equal to theEPAP.

Inspiratory positive airway pressure (IPAP): Maximum desired maskpressure which the ventilator will attempt to achieve during theinspiratory portion of the breath.

Pressure support: A number that is indicative of the increase inpressure during ventilator inspiration over that during ventilatorexpiration, and generally means the difference in pressure between themaximum value during inspiration and the base pressure (e.g.,PS=IPAP−EPAP). In some contexts pressure support means the differencewhich the ventilator aims to achieve, rather than what it actuallyachieves.

Servo-ventilator: A ventilator that measures patient ventilation, has atarget ventilation, and which adjusts the level of pressure support tobring the patient ventilation towards the target ventilation.

Spontaneous/Timed (S/T): A mode of a ventilator or other device thatattempts to detect the initiation of a breath of a spontaneouslybreathing patient. If however, the device is unable to detect a breathwithin a predetermined period of time, the device will automaticallyinitiate delivery of the breath.

Swing: Equivalent term to pressure support.

Triggered: When a ventilator delivers a breath of air to a spontaneouslybreathing patient, it is said to be triggered to do so at the initiationof the respiratory portion of the breathing cycle by the patient'sefforts.

Typical recent ventilation: The typical recent ventilation Vtyp is thevalue around which recent measures of ventilation over somepredetermined timescale tend to cluster. For example, a measure of thecentral tendency of the measures of ventilation over recent history maybe a suitable value of a typical recent ventilation.

4.4.4 Anatomy

4.4.4.1 Anatomy of the Face

Ala: the external outer wall or “wing” of each nostril (plural: alar)

Alar Angle:

Alare: The most lateral point on the nasal ala.

Alar curvature (or alar crest) point: The most posterior point in thecurved base line of each ala, found in the crease formed by the union ofthe ala with the cheek.

Auricle: The whole external visible part of the ear.

(nose) Bony framework: The bony framework of the nose comprises thenasal bones, the frontal process of the maxillae and the nasal part ofthe frontal bone.

(nose) Cartilaginous framework: The cartilaginous framework of the nosecomprises the septal, lateral, major and minor cartilages.

Columella: the strip of skin that separates the nares and which runsfrom the pronasale to the upper lip.

Columella angle: The angle between the line drawn through the midpointof the nostril aperture and a line drawn perpendicular to the Frankforthorizontal while intersecting subnasale.

Frankfort horizontal plane: A line extending from the most inferiorpoint of the orbital margin to the left tragion. The tragion is thedeepest point in the notch superior to the tragus of the auricle.

Glabella: Located on the soft tissue, the most prominent point in themidsagittal plane of the forehead.

Lateral nasal cartilage: A generally triangular plate of cartilage. Itssuperior margin is attached to the nasal bone and frontal process of themaxilla, and its inferior margin is connected to the greater alarcartilage.

Greater alar cartilage: A plate of cartilage lying below the lateralnasal cartilage. It is curved around the anterior part of the naris. Itsposterior end is connected to the frontal process of the maxilla by atough fibrous membrane containing three or four minor cartilages of theala.

Nares (Nostrils): Approximately ellipsoidal apertures forming theentrance to the nasal cavity. The singular form of nares is naris(nostril). The nares are separated by the nasal septum.

Naso-labial sulcus or Naso-labial fold: The skin fold or groove thatruns from each side of the nose to the corners of the mouth, separatingthe cheeks from the upper lip.

Naso-labial angle: The angle between the columella and the upper lip,while intersecting subnasale.

Otobasion inferior: The lowest point of attachment of the auricle to theskin of the face.

Otobasion superior: The highest point of attachment of the auricle tothe skin of the face.

Pronasale: the most protruded point or tip of the nose, which can beidentified in lateral view of the rest of the portion of the head.

Philtrum: the midline groove that runs from lower border of the nasalseptum to the top of the lip in the upper lip region.

Pogonion: Located on the soft tissue, the most anterior midpoint of thechin.

Ridge (nasal): The nasal ridge is the midline prominence of the nose,extending from the Sellion to the Pronasale.

Sagittal plane: A vertical plane that passes from anterior (front) toposterior (rear) dividing the body into right and left halves.

Sellion: Located on the soft tissue, the most concave point overlyingthe area of the frontonasal suture.

Septal cartilage (nasal): The nasal septal cartilage forms part of theseptum and divides the front part of the nasal cavity.

Subalare: The point at the lower margin of the alar base, where the alarbase joins with the skin of the superior (upper) lip.

Subnasal point: Located on the soft tissue, the point at which thecolumella merges with the upper lip in the midsagittal plane.

Supramenton: The point of greatest concavity in the midline of the lowerlip between labrale inferius and soft tissue pogonion

4.4.4.2 Anatomy of the Skull

Frontal bone: The frontal bone includes a large vertical portion, thesquama frontalis, corresponding to the region known as the forehead.

Mandible: The mandible forms the lower jaw. The mental protuberance isthe bony protuberance of the jaw that forms the chin.

Maxilla: The maxilla forms the upper jaw and is located above themandible and below the orbits. The frontal process of the maxillaprojects upwards by the side of the nose, and forms part of its lateralboundary.

Nasal bones: The nasal bones are two small oblong bones, varying in sizeand form in different individuals; they are placed side by side at themiddle and upper part of the face, and form, by their junction, the“bridge” of the nose.

Nasion: The intersection of the frontal bone and the two nasal bones, adepressed area directly between the eyes and superior to the bridge ofthe nose.

Occipital bone: The occipital bone is situated at the back and lowerpart of the cranium. It includes an oval aperture, the foramen magnum,through which the cranial cavity communicates with the vertebral canal.The curved plate behind the foramen magnum is the squama occipitalis.

Orbit: The bony cavity in the skull to contain the eyeball.

Parietal bones: The parietal bones are the bones that, when joinedtogether, form the roof and sides of the cranium.

Temporal bones: The temporal bones are situated on the bases and sidesof the skull, and support that part of the face known as the temple.

Zygomatic bones: The face includes two zygomatic bones, located in theupper and lateral parts of the face and forming the prominence of thecheek.

4.4.4.3 Anatomy of the Respiratory System

Diaphragm: A sheet of muscle that extends across the bottom of the ribcage. The diaphragm separates the thoracic cavity, containing the heart,lungs and ribs, from the abdominal cavity. As the diaphragm contractsthe volume of the thoracic cavity increases and air is drawn into thelungs.

Larynx: The larynx, or voice box houses the vocal folds and connects theinferior part of the pharynx (hypopharynx) with the trachea.

Lungs: The organs of respiration in humans. The conducting zone of thelungs contains the trachea, the bronchi, the bronchioles, and theterminal bronchioles. The respiratory zone contains the respiratorybronchioles, the alveolar ducts, and the alveoli.

Nasal cavity: The nasal cavity (or nasal fossa) is a large air filledspace above and behind the nose in the middle of the face. The nasalcavity is divided in two by a vertical fin called the nasal septum. Onthe sides of the nasal cavity are three horizontal outgrowths callednasal conchae (singular “concha”) or turbinates. To the front of thenasal cavity is the nose, while the back blends, via the choanae, intothe nasopharynx.

Pharynx: The part of the throat situated immediately inferior to (below)the nasal cavity, and superior to the oesophagus and larynx. The pharynxis conventionally divided into three sections: the nasopharynx(epipharynx) (the nasal part of the pharynx), the oropharynx(mesopharynx) (the oral part of the pharynx), and the laryngopharynx(hypopharynx).

4.4.5 Patient Interface

Anti-asphyxia valve (AAV): The component or sub-assembly of a masksystem that, by opening to atmosphere in a failsafe manner, reduces therisk of excessive CO₂ rebreathing by a patient.

Elbow: An elbow is an example of a structure that directs an axis offlow of air travelling therethrough to change direction through anangle. In one form, the angle may be approximately 90 degrees. Inanother form, the angle may be more, or less than 90 degrees. The elbowmay have an approximately circular cross-section. In another form theelbow may have an oval or a rectangular cross-section. In certain formsan elbow may be rotatable with respect to a mating component, e.g. about360 degrees. In certain forms an elbow may be removable from a matingcomponent, e.g. via a snap connection. In certain forms, an elbow may beassembled to a mating component via a one-time snap during manufacture,but not removable by a patient.

Frame: Frame will be taken to mean a mask structure that bears the loadof tension between two or more points of connection with a headgear. Amask frame may be a non-airtight load bearing structure in the mask.However, some forms of mask frame may also be air-tight.

Headgear: Headgear will be taken to mean a form of positioning andstabilizing structure designed for use on a head. For example theheadgear may comprise a collection of one or more struts, ties andstiffeners configured to locate and retain a patient interface inposition on a patient's face for delivery of respiratory therapy. Someties are formed of a soft, flexible, elastic material such as alaminated composite of foam and fabric.

Membrane: Membrane will be taken to mean a typically thin element thathas, preferably, substantially no resistance to bending, but hasresistance to being stretched.

Plenum chamber: a mask plenum chamber will be taken to mean a portion ofa patient interface having walls at least partially enclosing a volumeof space, the volume having air therein pressurised above atmosphericpressure in use. A shell may form part of the walls of a mask plenumchamber.

Seal: May be a noun form (“a seal”) which refers to a structure, or averb form (“to seal”) which refers to the effect. Two elements may beconstructed and/or arranged to ‘seal’ or to effect ‘sealing’therebetween without requiring a separate ‘seal’ element per se.

Shell: A shell will be taken to mean a curved, relatively thin structurehaving bending, tensile and compressive stiffness. For example, a curvedstructural wall of a mask may be a shell. In some forms, a shell may befaceted. In some forms a shell may be airtight. In some forms a shellmay not be airtight.

Stiffener: A stiffener will be taken to mean a structural componentdesigned to increase the bending resistance of another component in atleast one direction.

Strut: A strut will be taken to be a structural component designed toincrease the compression resistance of another component in at least onedirection.

Swivel (noun): A subassembly of components configured to rotate about acommon axis, preferably independently, preferably under low torque. Inone form, the swivel may be constructed to rotate through an angle of atleast 360 degrees. In another form, the swivel may be constructed torotate through an angle less than 360 degrees. When used in the contextof an air delivery conduit, the sub-assembly of components preferablycomprises a matched pair of cylindrical conduits. There may be little orno leak flow of air from the swivel in use.

Tie (noun): A structure designed to resist tension.

Vent: (noun): A structure that allows a flow of air from an interior ofthe mask, or conduit, to ambient air for clinically effective washout ofexhaled gases. For example, a clinically effective washout may involve aflow rate of about 10 litres per minute to about 100 litres per minute,depending on the mask design and treatment pressure.

4.4.6 Shape of Structures

Products in accordance with the present technology may comprise one ormore three-dimensional mechanical structures, for example a mask cushionor an impeller. The three-dimensional structures may be bounded bytwo-dimensional surfaces. These surfaces may be distinguished using alabel to describe an associated surface orientation, location, function,or some other characteristic. For example a structure may comprise oneor more of an anterior surface, a posterior surface, an interior surfaceand an exterior surface. In another example, a seal-forming structuremay comprise a face-contacting (e.g. outer) surface, and a separatenon-face-contacting (e.g. underside or inner) surface. In anotherexample, a structure may comprise a first surface and a second surface.

To facilitate describing the shape of the three-dimensional structuresand the surfaces, we first consider a cross-section through a surface ofthe structure at a point, p. See FIG. 3B to FIG. 3F, which illustrateexamples of cross-sections at point p on a surface, and the resultingplane curves. FIGS. 3B to 3F also illustrate an outward normal vector atp. The outward normal vector at p points away from the surface. In someexamples we describe the surface from the point of view of an imaginarysmall person standing upright on the surface.

4.4.6.1 Curvature in One Dimension

The curvature of a plane curve at p may be described as having a sign(e.g. positive, negative) and a magnitude (e.g. 1/radius of a circlethat just touches the curve at p).

Positive curvature: If the curve at p turns towards the outward normal,the curvature at that point will be taken to be positive (if theimaginary small person leaves the point p they must walk uphill). SeeFIG. 3B (relatively large positive curvature compared to FIG. 3C) andFIG. 3C (relatively small positive curvature compared to FIG. 3B). Suchcurves are often referred to as concave.

Zero curvature: If the curve at p is a straight line, the curvature willbe taken to be zero (if the imaginary small person leaves the point p,they can walk on a level, neither up nor down). See FIG. 3D.

Negative curvature: If the curve at p turns away from the outwardnormal, the curvature in that direction at that point will be taken tobe negative (if the imaginary small person leaves the point p they mustwalk downhill). See FIG. 3E (relatively small negative curvaturecompared to FIG. 3F) and FIG. 3F (relatively large negative curvaturecompared to FIG. 3E). Such curves are often referred to as convex.

4.4.6.2 Curvature of Two Dimensional Surfaces

A description of the shape at a given point on a two-dimensional surfacein accordance with the present technology may include multiple normalcross-sections. The multiple cross-sections may cut the surface in aplane that includes the outward normal (a “normal plane”), and eachcross-section may be taken in a different direction. Each cross-sectionresults in a plane curve with a corresponding curvature. The differentcurvatures at that point may have the same sign, or a different sign.Each of the curvatures at that point has a magnitude, e.g. relativelysmall. The plane curves in FIGS. 3B to 3F could be examples of suchmultiple cross-sections at a particular point.

Principal curvatures and directions: The directions of the normal planeswhere the curvature of the curve takes its maximum and minimum valuesare called the principal directions. In the examples of FIG. 3B to FIG.3F, the maximum curvature occurs in FIG. 3B, and the minimum occurs inFIG. 3F, hence FIG. 3B and FIG. 3F are cross sections in the principaldirections. The principal curvatures at p are the curvatures in theprincipal directions.

Region of a surface: A connected set of points on a surface. The set ofpoints in a region may have similar characteristics, e.g. curvatures orsigns.

Saddle region: A region where at each point, the principal curvatureshave opposite signs, that is, one is positive, and the other is negative(depending on the direction to which the imaginary person turns, theymay walk uphill or downhill).

Dome region: A region where at each point the principal curvatures havethe same sign, e.g. both positive (a “concave dome”) or both negative (a“convex dome”).

Cylindrical region: A region where one principal curvature is zero (or,for example, zero within manufacturing tolerances) and the otherprincipal curvature is non-zero.

Planar region: A region of a surface where both of the principalcurvatures are zero (or, for example, zero within manufacturingtolerances).

Edge of a surface: A boundary or limit of a surface or region.

Path: In certain forms of the present technology, ‘path’ will be takento mean a path in the mathematical—topological sense, e.g. a continuousspace curve from f(0) to f(1) on a surface. In certain forms of thepresent technology, a ‘path’ may be described as a route or course,including e.g. a set of points on a surface. (The path for the imaginaryperson is where they walk on the surface, and is analogous to a gardenpath).

Path length: In certain forms of the present technology, ‘path length’will be taken to mean the distance along the surface from f(0) to f(1),that is, the distance along the path on the surface. There may be morethan one path between two points on a surface and such paths may havedifferent path lengths. (The path length for the imaginary person wouldbe the distance they have to walk on the surface along the path).

Straight-line distance: The straight-line distance is the distancebetween two points on a surface, but without regard to the surface. Onplanar regions, there would be a path on the surface having the samepath length as the straight-line distance between two points on thesurface. On non-planar surfaces, there may be no paths having the samepath length as the straight-line distance between two points. (For theimaginary person, the straight-line distance would correspond to thedistance ‘as the crow flies’.)

4.4.6.3 Space Curves

Space curves: Unlike a plane curve, a space curve does not necessarilylie in any particular plane. A space curve may be closed, that is,having no endpoints. A space curve may be considered to be aone-dimensional piece of three-dimensional space. An imaginary personwalking on a strand of the DNA helix walks along a space curve. Atypical human left ear comprises a helix, which is a left-hand helix,see FIG. 3Q. A typical human right ear comprises a helix, which is aright-hand helix, see FIG. 3R. FIG. 3S shows a right-hand helix. Theedge of a structure, e.g. the edge of a membrane or impeller, may followa space curve. In general, a space curve may be described by a curvatureand a torsion at each point on the space curve. Torsion is a measure ofhow the curve turns out of a plane. Torsion has a sign and a magnitude.The torsion at a point on a space curve may be characterised withreference to the tangent, normal and binormal vectors at that point.

Tangent unit vector (or unit tangent vector): For each point on a curve,a vector at the point specifies a direction from that point, as well asa magnitude. A tangent unit vector is a unit vector pointing in the samedirection as the curve at that point. If an imaginary person were flyingalong the curve and fell off her vehicle at a particular point, thedirection of the tangent vector is the direction she would betravelling.

Unit normal vector. As the imaginary person moves along the curve, thistangent vector itself changes. The unit vector pointing in the samedirection that the tangent vector is changing is called the unitprincipal normal vector. It is perpendicular to the tangent vector.

Binormal unit vector: The binormal unit vector is perpendicular to boththe tangent vector and the principal normal vector. Its direction may bedetermined by a right-hand rule (see e.g. FIG. 3P), or alternatively bya left-hand rule (FIG. 3O).

Osculating plane: The plane containing the unit tangent vector and theunit principal normal vector. See FIGS. 3O and 3P.

Torsion of a space curve: The torsion at a point of a space curve is themagnitude of the rate of change of the binormal unit vector at thatpoint. It measures how much the curve deviates from the osculatingplane. A space curve which lies in a plane has zero torsion. A spacecurve which deviates a relatively small amount from the osculating planewill have a relatively small magnitude of torsion (e.g. a gently slopinghelical path). A space curve which deviates a relatively large amountfrom the osculating plane will have a relatively large magnitude oftorsion (e.g. a steeply sloping helical path). With reference to FIG.3S, since T2>T1, the magnitude of the torsion near the top coils of thehelix of FIG. 3S is greater than the magnitude of the torsion of thebottom coils of the helix of FIG. 3S

With reference to the right-hand rule of FIG. 3P, a space curve turningtowards the direction of the right-hand binormal may be considered ashaving a right-hand positive torsion (e.g. a right-hand helix as shownin FIG. 3S). A space curve turning away from the direction of theright-hand binormal may be considered as having a right-hand negativetorsion (e.g. a left-hand helix).

Equivalently, and with reference to a left-hand rule (see FIG. 3O), aspace curve turning towards the direction of the left-hand binormal maybe considered as having a left-hand positive torsion (e.g. a left-handhelix). Hence left-hand positive is equivalent to right-hand negative.See FIG. 3T.

4.4.6.4 Holes

A surface may have a one-dimensional hole, e.g. a hole bounded by aplane curve or by a space curve. Thin structures (e.g. a membrane) witha hole, may be described as having a one-dimensional hole. See forexample the one dimensional hole in the surface of structure shown inFIG. 3I, bounded by a plane curve.

A structure may have a two-dimensional hole, e.g. a hole bounded by asurface. For example, an inflatable tyre has a two dimensional holebounded by the interior surface of the tyre. In another example, abladder with a cavity for air or gel could have a two-dimensional hole.See for example the cushion of FIG. 3L and the example cross-sectionstherethrough in FIG. 3M and FIG. 3N, with the interior surface boundinga two dimensional hole indicated. In a yet another example, a conduitmay comprise a one-dimension hole (e.g. at its entrance or at its exit),and a two-dimension hole bounded by the inside surface of the conduit.See also the two dimensional hole through the structure shown in FIG.3K, bounded by a surface as shown.

4.5 Other Remarks

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in Patent Office patent files orrecords, but otherwise reserves all copyright rights whatsoever.

Unless the context clearly dictates otherwise and where a range ofvalues is provided, it is understood that each intervening value, to thetenth of the unit of the lower limit, between the upper and lower limitof that range, and any other stated or intervening value in that statedrange is encompassed within the technology. The upper and lower limitsof these intervening ranges, which may be independently included in theintervening ranges, are also encompassed within the technology, subjectto any specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the technology.

Furthermore, where a value or values are stated herein as beingimplemented as part of the technology, it is understood that such valuesmay be approximated, unless otherwise stated, and such values may beutilized to any suitable significant digit to the extent that apractical technical implementation may permit or require it.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this technology belongs. Although any methods andmaterials similar or equivalent to those described herein can also beused in the practice or testing of the present technology, a limitednumber of the exemplary methods and materials are described herein.

When a particular material is identified as being used to construct acomponent, obvious alternative materials with similar properties may beused as a substitute. Furthermore, unless specified to the contrary, anyand all components herein described are understood to be capable ofbeing manufactured and, as such, may be manufactured together orseparately.

It must be noted that as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include their plural equivalents,unless the context clearly dictates otherwise.

All publications mentioned herein are incorporated herein by referencein their entirety to disclose and describe the methods and/or materialswhich are the subject of those publications. The publications discussedherein are provided solely for their disclosure prior to the filing dateof the present application. Nothing herein is to be construed as anadmission that the present technology is not entitled to antedate suchpublication by virtue of prior invention. Further, the dates ofpublication provided may be different from the actual publication dates,which may need to be independently confirmed.

The terms “comprises” and “comprising” should be interpreted asreferring to elements, components, or steps in a non-exclusive manner,indicating that the referenced elements, components, or steps may bepresent, or utilized, or combined with other elements, components, orsteps that are not expressly referenced.

The subject headings used in the detailed description are included onlyfor the ease of reference of the reader and should not be used to limitthe subject matter found throughout the disclosure or the claims. Thesubject headings should not be used in construing the scope of theclaims or the claim limitations.

Although the technology herein has been described with reference toparticular examples, it is to be understood that these examples aremerely illustrative of the principles and applications of thetechnology. In some instances, the terminology and symbols may implyspecific details that are not required to practice the technology. Forexample, although the terms “first” and “second” may be used, unlessotherwise specified, they are not intended to indicate any order but maybe utilised to distinguish between distinct elements. Furthermore,although process steps in the methodologies may be described orillustrated in an order, such an ordering is not required. Those skilledin the art will recognize that such ordering may be modified and/oraspects thereof may be conducted concurrently or even synchronously.

It is therefore to be understood that numerous modifications may be madeto the illustrative examples and that other arrangements may be devisedwithout departing from the spirit and scope of the technology.

4.6 Reference Signs List

-   1000 patient-   1100 bed partner-   3000 patient interface-   3100 seal-forming structure-   3200 plenum chamber-   3300 structure-   3400 vent-   3402 passage-   3404 wall-   3406 diffusing material-   3408 housing-   3410 air passage-   3412 gap-   3412A second portion-   3414 surface-   3416 opening-   3418 portion-   3420 opening-   3422 arrow-   3424 opening-   3426 member-   3428 wall-   3430 center line-   3432 center line-   3434 support-   3436 lateral surface-   3438 groove-   3440 cover-   3442 deflector-   3600 connection port-   3700 forehead support-   4000 RPT device-   4170 air circuit-   5000 humidifier

The invention claimed is:
 1. A gas washout vent for a patient interfacesystem configured to maintain a therapy pressure in a range of about 4cmH2O to about 30 cmH2O above ambient air pressure in use, throughout apatient's respiratory cycle, while the patient is sleeping, toameliorate a respiratory or a sleep disordered breathing condition, thegas washout vent comprising: a housing comprising a first wall with oneor more passages through the first wall, the one or more passages beingconfigured to provide fluid communication with a portion of the patientinterface system that is configured to be exposed to the therapypressure, the one or more passages each including a respective firstopening on a first surface of the first wall, the housing at leastpartially defining a second opening that is in communication withambient atmosphere; and a diffusing material located at least partiallywithin the housing to be adjacent the first surface, a surface of thediffusing material facing the first surface being spaced away from thefirst surface by a gap that extends to provide fluid communicationbetween all of the first openings, as well as between all of the firstopenings and the second opening; wherein the housing further comprises athird opening in communication with ambient atmosphere; the thirdopening does not overlap with an area of an outlet of any of thepassages that is projected along a central axis of the respectivepassages, and is located so that at least part of the diffusing materialis between each first opening and the third opening; the housing isconfigured so that air is prevented from flowing out of the housing atall areas directly opposite each of the first openings; and thediffusing material and a material of the first wall are differentmaterials.
 2. The gas washout vent according to claim 1, wherein thethird opening is oriented so that a central axis through the thirdopening is angled with respect to the central axis of any of thepassages.
 3. The gas washout vent according to claim 2, wherein thethird opening is sized so that completely blocking the third openingdoes not substantially decrease the air flow through the gas washoutvent when the portion of the patient interface is exposed to the therapypressure.
 4. The gas washout vent according to claim 3, wherein the airflow through the gas washout vent does not decrease by more than threepercent.
 5. The gas washout vent according to claim 1, wherein the thirdopening is one of a plurality of third openings.
 6. The gas washout ventaccording to claim 1, wherein the third opening is configured for waterremoval.
 7. The gas washout vent according to claim 1, wherein thesecond opening comprises a plurality of second openings.
 8. The gaswashout vent according to claim 1, wherein at least one of the one ormore passages are sized so that at least a portion of air exiting therespective first opening penetrates into the diffusing material when theportion of the patient interface is exposed to the therapy pressure. 9.The gas washout vent according to claim 8, wherein the gas washout ventis configured so that the portion of the air penetrating the diffusingmaterial exits the diffusing material and re-enters the gap beforeflowing out of the second opening.
 10. The gas washout vent according toclaim 8, wherein the gas washout vent is configured so that the portionof the air exiting the respective first opening penetrates and exits thediffusing material via the surface.
 11. The gas washout vent accordingto claim 1, wherein no more than 28 dB(A) noise is generated when airexits the second opening as a result of the portion of the patientinterface being exposed to the therapy pressure.
 12. The gas washoutvent according to claim 1, wherein the diffusing material comprisesuncompressed fibers.
 13. The gas washout vent according to claim 1,wherein the diffusing material comprises moisture wicking material. 14.The gas washout vent according to claim 13, wherein the moisture wickingmaterial is sintered plastic.
 15. The gas washout vent according toclaim 1, wherein the diffusing material comprises hydrophobic material.16. The gas washout vent according to claim 1, wherein the diffusingmaterial possesses antibacterial properties.
 17. The gas washout ventaccording to claim 1, wherein the first wall is fixed in the housing ina non-releasable manner.
 18. The gas washout vent according to claim 1,wherein the gap is at least partially bounded by the first wall from thefirst openings to the second opening.
 19. The gas washout vent accordingto claim 18, wherein the gap is formed by the surface from a locationopposed to the first openings to a portion of the diffusing materialthat is closest to the second opening.
 20. The gas washout ventaccording to claim 1, wherein the gap is tapered in a radial direction.